All are taken from this site.http://www.teletopix.org/cdma/why-closed-loop-power-control-in-cdma/

List of Parameters and Terms for PN Offset Planning in CDMAThere are various parameters and terms which come into play when discussing PN offsets and their function in CDMA.System TimeAll base station digital transmissions are referenced to a common CDMA system-wide time scale that uses the Global Positioning System (GPS) time scale, which is traceable to and synchronous with Universal Coordinated Time (UTC).Time ReferenceThe mobile station shall establish a time reference which is used to derive system time. This time reference will be the earliest arriving multipath component being used for demodulation.This reflects the assumption that the mobile stations fix on system time is always skewed by delay associated with the shortestactivelink.PILOT_PNThe Pilot PN sequence offset (index), in units of 64 PN chips. It ranges from 0 to 511. Every transmit sector will have an offset assigned to it. This parameter is set for each sector in the pilotpn field.Active SetThe pilots associated with theForwardTrafficChannels assigned to the mobile station.It is the base station that assigns all active set pilots to mobile stations.Candidate SetThe pilots that are not currently in the Active Set but have been received by the mobile station with sufficient strength to indicate that the associated Forward Traffic Channels could be successfully demodulated. As a property of the Mobile AssistedHandOff(MAHO), the mobile station promotes aNeighborSet or Remaining Set pilot to the Candidate Set when certain pilot strength criteria are met and then recommends the pilot to the base station for inclusion in the Active Set.Neighbor SetThe pilots that are not currently in the Active Set or the Candidate Set and are likely candidates for handoff. Neighbor Set pilots are identified by the base station via Neighbor List and Neighbor List Update messages.Remaining SetThe set of all possible pilots in the current system on the current CDMAfrequencyassignment, excluding pilots in the other sets. These pilots must be integer multiples of PILOT_INC.SRCH_WIN_N, SRCH_WIN_RThese parameters represent thesearch windowsizes associated with Neighbor Set and Remaining Set pilots.The mobile station centers the search window for each pilot around the pilots PN sequence offset using timing defined by the mobile stations time reference. In general, a neighbor search window, SRCH_WIN_N, will be sized so as to encompass the geographic area in which the neighbor may be added (a soft handoff add zone or initial detection area). The largest a neighbor search window need be is sufficient to cover the distance between the neighbors, , plus an accommodation of the time-of-flight delay (approx. 3 chips).SRCH_WIN_AThis parameter represents the search window size associated with the Active Set and Candidate Set pilots.The mobile station centers the search window for each pilot around the earliest arriving usable multipath component of the pilot. Note that in contrast to the neighbor or remaining set search windows, the active/candidate search windows float with the desired signals. That is to say that the center position of the search window is updated every scan to track the new location of the earliest arriving multipath component.To better illustrate the relationships between search windows, consider the following scenario:A mobile station monitors a neighbor pilot. The neighbor search window is centered on the neighbor pilot offset. This centering is relative based on timing derived from the time reference. When the pilot strength of a neighbor pilot recommends promotion to the candidate set, then the search window will be tightened to the active search window size. The active search window is sized to compensate for delay spread only and is, therefore, smaller than the neighbor search window. In addition, the active search window locks onto and tracks the candidate pilot.PILOT_ARRIVALThe pilot arrival time is the time of occurrence of the earliest arriving usable multipath component of a pilot relative to the mobile stations time reference.PILOT_PN_PHASEThe mobile station reports pilot strength and phase measurements for each active and candidate pilot in the Pilot Strength Measurement Message when recommending a change in the handoff System Time status (i.e. mobile assisted handoff). The mobile station computes the reported PILOT_PN_PHASE as a function of the PILOT_ARRIVAL and the PILOT_PN.The pilot arrival component represents the time delay of the pilot relative to the time reference or, in other words, how skewed the pilot is from the mobiles concept of system time. Both the PILOT_ARRIVAL and PILOT_PN_PHASE measurements are in chips (15 bits, 0 to 32,767 or 215-1) while the PILOT_PN is in offsets (9 bits, 0 to 511). The difference (6 bits) corresponds to the 64 chip intervalbetween successive PN offsets.Note also that the mobile does not identify pilots by their offset index directly, but by their phase measurement. If the pilot arrival was larger than 32 chips (1/2 of a pilot offset or 4.8 miles), then this could undermine the ability of the base station to properly translate pilot phase into pilot offset index (given a PILOT_INC of 1).PILOT_INCThe pilot PN sequence offset index increment is the interval between pilots, in increments of 64 chips. Its valid range is from 1 to 15.The mobile station uses this parameter in only one manner, to determine which pilots to scan from among the Remaining set. Only valid pilots (i.e. those pilots that are multiples of PILOT_INC) will be scanned. For the mobile station, PILOT_INC impacts only the scanning rate applied to Remaining pilots. It accomplishes this by reducing the number of Remaining pilots that need to be scanned.For the base station, its effect is different. In the base station, it is used in properly translating pilot phase back into pilot offset index. The consequence is that the operator may artificially increase the separation between valid time offsets. By selecting a PILOT_INC of 2, for instance, an operator chooses to limit the number of valid offsets to 256 (i.e. 0, 2, 4,, 508, 510) instead of 512. The increased separation means that the pilot arrival must be larger before adjacent offset ambiguity is possible and consequently the likelihood of a strong adjacent interferer is reduced.What is the Result of Incorrect PN Planning in CDMA ?The design of a PN offset plan for CDMA is comparable to that of a signallingchannelfrequencyplan in analog. The consequences of poor offset planning include the following:ActiveSet PilotInterference-This phenomenon would occur in the active area and involve the activesearch window(SRCH_WIN_A). The interfering signal would need to be strong enough to be processed as an active finger (except in the less likely case where the timing was perfectly coincident with a true active finger).NeighborSet Pilot Falsing -A neighbor set pilot may falsely appear strong enough for the mobile station (MS) to promote the pilot to the candidate set and recommend to the base station (BS) to perform a softhandoffadd via the Pilot Strength Measurement Message (PSMM). This falsing would occur in the neighbor area and involve the neighbor search window (SRCH_WIN_N). The falsing signal strength would need to meet the T_ADD threshold criteria.The probability for interference or falsing is dependent upon two factors: timing and strength. Time differentials can be translated into geographic regions and have as their threshold the search window size. A detailed discussion of this topic will be found laterwithin this chapter. If a signal falls outside of a search window, its energy becomes nothing more than uncorrelated interference.Note that the term active area is meant to refer to the area in which a signal may be (or is intended to be) actively demodulated. The term neighbor area refers to the area in which a signal will be sought as a candidate. In geographic terms, the neighbor area greatly expands the region where problems may occur since we search for a neighbor signal in many areas outside of the active area.The use of large or generous neighbor lists along with the technique of merging neighbor lists when in soft/softer handoff creates further expansion. Mitigating this expansion of the geographic space in which falsing may occur is the heightened signal strength threshold at which interference may occur (a T_ADD of -14dB versus a finger-locking threshold of approximately -24dB).Incorrect BS Identification -A signal may travel far enough to be incorrectly identified by the BS when it translates the MS reported phase into a PILOT_PN offset index.

Interference Margin for CDMAIn determining RF coverage inCDMAsystems, the effect ofinterferencegenerated from the servingcellas well as the neighboring cells must be considered, this is in contrast to the RF coverage analysis for AMPS cells where interference mainly affects thefrequencyassignment but not the coverage.The interference margin is dependent upon the amount of loading assumed in thesystem. Different cell deployment strategies can be modeled by varying the interference margin. CDMA cell deployments could be based on loading individual frequencies one by one, until they achieve the target load (for instance, a 6 dB noise rise). An alternative deployment could utilize more CDMAradiocarriers, initially operating at a reduced load, to further extend the range of the cells (for instance, 3 dB noise rise) while trading off capacity (exploiting any immediate spectrum available). This 3 dB system rise improvement would result in approximately 30% fewer CDMA cell sites at system turn-on.The following equation can be used as a first pass approximation to the amount of interference margin one should add to the link budget to account for loading the CDMA system with users.NoiseRise = 10 log [1/(1-X)]Where X is the maximum allowed number of users, specified as a fraction of pole capacity. For example, a capacity cell site has X equal to seventy-five percent (75%). Noise rise varies as a function of propagation, environment, load, user distribution, etc.CDMA Traffic Channel Definitions Effective Traffic,Actual Traffic and Physical TrafficTrafficChannelDefinitionsIn analog systems, the traffic channels (or voice channels) are synonymous with thephysicaltransceiver hardware. The nature of CDMA technology implies that the effective traffic carrying capacity of a CDMA carrier varies in accordance with theinterferencedensity in the band and also depends on various CDMA system parameters. From the hardware perspective, the physical transceivers are the same for all channel types meaning that the sync, paging and the traffic channels are all supported by identical hardware.The transceiver elements could be used for handling incoming traffic, supporting soft handoff or configured as sync and paging channels. Using the guidelines provided earlier in this section, an engineer/system planner is able to derive the total number of cell sites needed to support the traffic capacity of a planned CDMA system and estimate the total Erlangs supported by each cell.However, for the purpose of equipment planning, it is desirable to convert the total Erlangs per cell to the number of transceiver elements required to support the calls (Physical TCHs). In order to convert Erlangs to Physical Traffic Channels (PTCH), the quantity of channels required to handle subscriber traffic, soft handoff and overhead messaging must be known. currently three principle traffic channel types.Effective Traffic Channels (ETCH)The Effective Traffic Channels (ETCH) are the quantity of channels required to support the primary traffic. The channel load associated with ETCH does not include the additional channel capacity required for soft handoff or overhead messaging. Note that in general, one ETCH corresponds to a single analog voice channel or one voicetimeslotof a TDMA carrier.As soft handoff is not included within the calculation for ETCH, the quantity of ETCHs can be considered the most relevant comparison of capacity with analog systems where no make-before-break handoff exists. The number of ETCHs are calculated by conversion from the total estimated Erlangs generated at a given Grade OfService(GOS) using the standard Erlang conversion tables.Actual Traffic Channels (ATCH)The Actual Traffic Channels (ATCH) are the quantity of channels required for the primary traffic plus those Erlangs to support soft handoff (SHO). SHO corresponds to additional Erlangs generated by the primary traffic not additional channels.For example, if the Effective Erlangs generated for a sector was 11.5 (using Erlang B at 2% GOS this converts to 18 ETCH), the conversion to ATCH assuming 35% SHO would be 11.5 x 0.35 = 4.025 + 11.5 = 15.52 Erlangs (using Erlang B at 2% GOS this converts to 24 ATCH).Physical Traffic Channels (PTCH)The Physical Traffic Channels (PTCH) are the total channels required for primary traffic, soft handoff (ATCH) plus OverHead (OH) messaging. The OH messaging corresponds to the channels required for paging and synchronization on theforwardlink and access on thereverselink. A total of two OH channels are required per CDMA sector.Therefore, an Omni directional (single sector) site requires 2 OH channels, while a three sector configuration requires 6 OH channels (2 per sector). Additional carriers within a sector may require more OH channels to be dedicated.CDMA Handoff Defination,Types and CapacityHandoffsThe TIA/EIA Interim Standard, Mobile Station Base Station Compatibility Standard of Dual- Mode Wideband Spread Spectrum CellularSystem(TIA/EIA/IS-95), states that a CDMA base station shall support three types ofhandoffprocesses.CDMA to CDMA Hard HandoffA CDMA to CDMA hard handoff is a handoff in which the base station directs the mobile station to transition between disjoint sets of base stations, differentfrequency assignments, or different frame offsets.CDMA to Analog Hard HandoffA CDMA to Analog hard handoff is a handoff in which the base station directs the mobile station from aForwardTCH to an analog voicechannel.Soft HandoffA soft handoff is a handoff in which a new base station commences communications with the subscriber station without interrupting the communications from the old base station. The base station can direct the subscriber station to perform a soft handoff only when all ForwardTrafficChannels assigned to the subscriber station have identical frequency assignments. While soft handoff is being performed, more than 1 TCH shall be assigned to the subscriber.Softer HandoffSubscribers in the overlapping region are power controlled by both sectors during softer-handoffs and their signals are coherently combined. The threshold for activation of this procedure is a systemcontrolparameter. Softer handoff mitigates both path loss differences due to different shadowing and fades. In the activated region, both sector antennas are engaged and received along opposite slopes of their patterns to help differentiate multipath components.Overhead Erlang Capacity for Soft HandoffThe soft handoff factor is used to determine the overhead Erlangs to support different kinds of soft handoffs. The factor is likely to vary from 1.3 to 2.0. It should be noted that the soft handoff factor (SHOF) defined here is a linear scaling factor of the actual usable Erlangs but not the number of traffic channels.Soft Handoff Factor = 1*(1-a-b) + 2*a + 3*bwhere:2-way soft Handoff fraction, a = Average two-way software handoff duration per access/hold time3-way soft Handoff fraction, b = Average three-way soft handoff duration per access /hold time

Reverse Channel Structure in CDMATheReverseCDMAChannelis composed of Access Channels and Reverse Traffic Channels. These channels share the same CDMAfrequencyassignment. Each Traffic Channel is identified by a distinct user long code sequence and each Access Channel is identified by a distinct Access Channel long code sequence. The following figure shows as example of the signals received by a base station on the Reverse CDMA Channel.

The reverse link employs the same 32768 length binary short PN sequences which are used for theforwardlink. However, unlike on the forward link, a fixed code phase offset is used. A long (242-1) PN sequence with a user-determined time offset is used to identify the subscriber (analogous to ESN in AMPS). The sequence is then modulo-2 added with a 42 bit wide mask.The subscriber unit convolutionally encodes the data transmitted on the Reverse Traffic Channel and the Access Channel prior tointerleaving. The transmitted digital information is convolutional encoded using a rate 1/3 code of constraint length 9 for the Access Channel and Rate Set 1 of the Reverse Traffic Channel. For Rate Set 2 of the Reverse Traffic channel, the convolutional code rate is 1/2.The encoded information is then interleaved over a 20 ms interval. The interleavedinformation is then grouped in code words which consist of 6 symbol groups each. These code words are used to select one of the 64orthogonalWalsh Codes fortransmission. On the reverse link, the Walsh Codes are used for information transmission. The reverse CDMA frequency channel can support up to 62 TCHs per Paging channel and 32 Access Channels per Paging Channel.

Forward Channel Structure in CDMAHere i write down on howForwardChannelworks in CDMA ? and its Structure. The following figure shows an example of the code channels transmitted by a base station. Out of the 64 code channels available for use, the example depicts the Pilot Channel (always required), one Sync channel, seven Paging Channels (the maximum allowed), and fifty-five Traffic Channels.Code channels on the forward link are addressed by different Walsh Codes. Each of these code channels is spread by the appropriate Pseudo-Noise Sequence at a fixed Chip Rate of 1.2288 Mega- Chips per second. The uniqueness of the forward channel structure is the use of the Pilot Channel.It is transmitted by each cell site and is used as a coherent carrier reference for demodulation by all subscriber stations. The pilot signal is unmodulated and uses the zeroth Walsh Code which consists of 64 zeros. Hence, the pilot simply contains the I and Q spreading code.The choice of this code allows the subscriber to acquire the system faster. The Walsh Codes are generated with a 64 x 64 Hadamard Matrix. Thus, the maximum number of code channels per carrier is 64 which consists of a Pilot Channel, a Sync Channel, a maximum of 7 Paging Channels and a minimum of 55 Traffic Channels (TCH).In view of the channel structure, a 1.23 MHz CDMA carrier can support up to 55 TCHs if the effect ofinterferenceis not considered. Another possible configuration could replace Paging Channels and Sync Channels one for one with TCHs to obtain a maximum of 63 TCHs, 1 Pilot Channel, 0 Paging Channel, and 0 Sync Channel. In practice, due to the intense interference in the spectrum, a satisfactory quality ofservicein terms of voice quality and FER is difficult to maintain if all 55 traffic channels are implemented in the system.The SCTM CDMA equipment requires a carrierfrequency, a pilot offset, and a Walsh Code to encode/decode the channel. The BSS allocates a traffic channel in response to the Assignment Request message from the MSC. BSS does not allocate traffic channels unless a request from the MSC is acknowledged. The traffic channel will be allocated in the sector with which the call is associated.The BSS maintains a pool of traffic channels and Walsh Codes in each sector for new call setups and soft/softer handoffs. Traffic channel allocation for new originations and soft handoffs require an assignment of aphysicaltraffic channel and a Walsh Code. Softer handoff requires just the assignment of a Walsh Code, no new traffic channel element has to be assigned. The assignment of Walsh Codes and traffic channels is separated to allow the allocation process to adjust for the different needs of soft and softer handoff. In order to reduce the risk of soft/softer handoff assignment failure during the conversation, the BSS denies assignment of traffic channels and Walsh Codes for new call setups if traffic channels or Walsh Codes are not available or being used for soft/softer handoffs.The number of traffic channels is defined by the In-Service Hardware in the BSS. It could be less than the number configured if some of the hardware is out of service. The number of Walsh Codes assigned to a sector is set to 64 which is the maximum specified by the EIA/TIA standard. Limiting the number of Walsh Codes in a sector is a method of controlling service quality. Since Walsh Codes are not associated with any hardware, they cannot go out of service. As a result, 64 is the hard limit of the number of code channels per sector according to theprotocolspecifications.

Conventional Blocking Analysis for CDMAConventional Blocking formula and its Analysis forcdma.In AMPS and TDMA systems, voice/trafficchannels are assigned to users aslongas they are available. Given the required offered traffic, the Erlang B model is used to determine the number of traffic channels required to provide a predetermined grade ofservice. The Erlang B model is based upon a model of serving without queuing. In other words, all blocked calls are cleared.Traffic load is the product of call rate and call holding time. It is a dimensionless quantitymeasured in Erlangs. One Erlang is the traffic intensity of a trafficchannelwhich is continuously occupied. Grade of service is a term used to quantify the extent to which congestion occurs in any trunkingsystemand is typically expressed as the probability of finding blocking. Blocking in AMPS and TDMA is defined to occur when all voice frequencies (for AMPS) or time slots (for TDMA) have been assigned to other subscriber stations.The values quoted for traffic load and grade of service for cellular systems are usually taken during the busy hour. Busy hour is defined as the continuous one-hour period in the day during which the highest average traffic density is experienced by the system.The Erlang B formula is given by:P blocking = (Ac/ci)/((cEk=0)*(Ak/Ki))whereA is the offered trafficC is the number of available serversAssumptions of the Erlang B Model:1. The number of potential users is infinite2. Intervals between originations are random3. Call holding times are random4. Call set up time is negligible

Soft Handoff Gain for CDMASofthandoffis the term that is normally associated with the fact that aCDMAsystemmakes a connection to a targetcellprior to releasing (breaking) from the source site, commonly referred to as make-before-break. A hard handoff, associated with AMPS, GSM, or USDC, requires that thesignalstrength from the target cell be greater than the signal strength from the source cell by a hysteresis value in order to reduce the number of handoffs per call and the ping-pong effect.This hysteresis requires an overlap between the cell coverage areas. The soft handoff gain corresponds to a decreased shadow fade margin required by the CDMA soft handoff over that of a hard handoff system. Some proponents of CDMA may have a separate entry in the RF link budget for soft handoff gain.The purpose of this is to provide information as to the benefits of CDMA over other technologies. Some factions believe that the soft handoff gain should be accounted for in the reliability value (shadow fade margin).For afixedsystem, the gain offered by soft handoff may or may not be present depending upon the system design. For instance, a single isolated site supporting a WiLL system would have no neighboring sites to even allow soft handoff to occur. In this situation, the soft handoff gain would be zero. Another situation is for a fixed system utilizing external FWT antennas.These antennas tend to be directional and would be sited to the best signal source and therefore minimal advantage from soft handoff would be recognized. Even for the situation of a fixed system using the FWT whip antennas, soft handoff gain may be lower than seen in a mobile environment. The FWT installation causes a form of building directionality which may decrease the soft handoff advantage.Power Control Inaccuracy in CDMACDMA means all depedancy onpower controlhere i write on PowerControlInaccuracy in cdma.Trafficcapacity of CDMA systems is increased by implementing an appropriate power control scheme to equalize the performance of all subscribers in thesystem. The appropriate power control scheme reduces theinterferenceto the other adjacent cells.The less interference generated in the spectrum, the more users the CDMA system can support. As previously mentioned, the inaccuracy in power control is roughly a log-normal distributed function. Under different path loss situations, the average required Eb/(N0+I0) tends to fluctuate around the mean to maintain a desirable Frame Error Rate. The power control standard deviation varies according to the extent of fluctuations.This graph shows that improving the accuracy of power control can provide some increase to the number of users.At relatively slow speeds or in static conditions (fixed), power control is effective in counteracting slow fades whereas at high speeds power control is not as effective in counteracting fast fading. At higher speed, the effects ofinterleavingbecome increasingly beneficial.

Defination and work of Eb/No in CDMAEb/No corresponds to energy per bit overinterferenceplus noise density for a given target FER (typical FER target is 1%). In digital communications, it is customary to designate one-sided noise density with No. In CDMA, interference is dominated by the noise generated due to other users in the system. Here No, is refers to the total power density due to interference and noise.Included in the CDMA Eb/No value isdiversityimprovement arising from performance in Rayleigh fading. This is distinct from the entry Soft Handoff Gain which represents an estimate of the performance improvement of soft handoff, relative to hard handoff, when experiencing log normal shadowing.In general, the requireddownlinkEb/No, to provide an acceptable audio quality, improves at higher speeds and in soft handoff. In the uplink path, the required Eb/No improves at lower speeds (reverseof downlink). The worst case Eb/No value for the uplink is at about 30 Kmph.The uplink Eb/No value accounts for rake (non-coherent combining)receiver, dualantenna, andinterleaving/coding. The downlink Eb/No value accounts for rake (coherent, maximal ratio combining), and interleaving/coding. For mobile systems, the Eb/No target varies dynamically as the mobile moves around. However, FWTs are fixed and the only movement is that of people around the FWT in a building and buses or pedestrians close to an outdoor FWT antenna.Optimized FWT deployment may significantly reduce the Eb/No target by avoiding the fading caused by the surrounding environment. In a mobile environment, the fading characteristic is Rayleigh. For a fixed system, the fading environment may be more Rician. The Eb/No value assumes a certain type of fading environment. The Eb/No requirement for a fixed system will therefore be different than for a mobile environment.The Eb/No target value can range from 4 dB to 8 dB for CDMA WLL systems. The Eb/No target value should be set to 8 dB for isolated cells using indoor omni FWT antennas or for cells with little SHO benefits in the fringe areas. However, if external directional FWT antennas are used and a Line Of Site (LOS) path exists between the cell site and the FWT antenna, an Eb/No target value of 4 dB may be used.As improvements are made to the hardware (chipsets) and to the software (how the energy is managed), the Eb/No requirement level may be lessened. Typical Eb/No values used for fixed systems are stated above. The current requirements for a mobile system are approximately 7 to 7.5 dB for the 8 kb and 13 kb vocoder respectively. From a link budget analysis, only one Eb/No value can be assumed for a given scenario. the Eb/No requirements needed to meet a desired frame error rate for each link that is being analyzed between the user and the site.Sectorization Gain in CDMASectorization gain can be somewhat of a misleading term. One could think of the sectorization gain as more of a reduction factor. For an omni site, the sectorization gain is one. With a sector site, one could initially try to multiply the resulting capacity of an omni site (or single sector) by the number of sectors for the sector site (i.e. a three sector site would support three times the number of users at an omni site and a six sector site would support six times the number of users at an omni site).This is not the case though. One can think of the additional sectors as being other locations generatinginterferenceto the desired sector. The othercellinterference factor accounts for just that, interference generated by other sites. The sectorization gain is the adjustment for the other sectors at the local site causing increased levels of interference. The reason it is referred to as a sectorization gain is that for a givenphysicalsite location, this site location is able to support many more users when it is sectorized than if it stayed omni.The sectorization gain can be improved by selecting antennas which have a good front to back ratio and which also exhibit a quick rolloff past the halfpowerpoints (3 dB down from main lobe). For instance, using a 90 degreeantennain place of a 120 degree antenna for a three sector site would decrease the amount of energy (interference) going into adjacent sectors, thus increasing the sectorization gain and thereby improving upon the number of users which could be supported.Though one can not decrease the horizontal beamwidth too far so as coverage (signalstrength) is not sufficient. As the sectorization gain increases, one can see from the following graph that the number of users will increases. The sectorization gain value which is commonly used is 0.8 per sector or 2.4 for a three sector site (0.8 time 3). This 0.8 sectorization gain can be thought of as a 1 dB impact to the capacity of the site due to other sectors interference.The above figure would apply only to a three sector site. The sectorization gain shown is for an entire site. For instance, a sectorization gain of 2.4 corresponds to 0.8 per each sector (= 2.4/3). For an omni site the sectorization gain would be 1. If one considered the sectorization per sector for a six sector site to be similar to a three sector site then the sectorization gain for the site would be 6 times the per sector value (for instance, 6 * 0.8 = 4.8).

CDMA Forward Channel Carrier PowerCDMAforwardchannelcarrierpower varies greatly depending on how many traffic channels are in use, the characteristics of the users voices, the ForwardPower Controlsettings as requested by each subscriber unit in use, and the power allocated for overhead functions (Pilot, Page and Sync).An approximation of the CDMA forward channel carrier power can be defined as the power under the following conditions:Number of Forward Links (or total Traffic Channels):the number of traffic channels required at the 2% Blocked-Calls-Cleared (Erlang B) Grade ofServicelevel plus the number of traffic channels that are in Soft Handoff with another cell, and/or in Softer Handoff with another sector of the same cell, i.e.,Nfl = N(2%) x SSHOF, where SSHOF is the Soft plus Softer Handoff FactorTraffic Channel power:The power of the average traffic channel due to averagemodulationplus full rate PowerControlBits, i.e., approximately 0.15 x Ppilot for Rate Set 1, and approximately 0.27 x Ppilot for Rate Set 2Forward Power Control:The average Forward Power Control setting, at this setting the average traffic channel power is still approximately 0.15 x Ppilot for Rate Set 1, and approximately 0.27 x Ppilot for Rate Set 2Overhead power:Pilot plus Page plus Sync power is equal to Ppilot plus 0.75 x Ppilot plus 0.1 x Ppilot = 1.85x PpilotSince the component parts of the CDMA carrier power are all expressed in terms of Pilot power, and since Pilot power is generally determined by the site coverage requirements, we may sum this up as follows:P(cdma) = Overhead power + Traffic Channel powerP(cdma) = 1.85 x Ppilot + Nfl x 0.15 x Ppilot (for Rate Set 1) or,P(cdma) = 1.85 x Ppilot + Nfl x 0.27 x Ppilot (for Rate Set 2)It must be realized that these formulas are approximations, since the power level of the Overhead components and the number and power level of the Traffic Channels continuously vary in the real world.What is Antenna Beamwidth ?Antennabeamwidth is measured in degrees between the halfpowerpoints (3 dB) of the major lobe of the antenna, Beamwidth can be expressed in terms of azimuth (horizontal or H-plane) and elevation (vertical or E-plane).The predominant type of antenna configuration within urban areas at PCS frequencies will be three sectored. This implies that each sector should utilize an antenna with 120 degree horizontal beamwidth, however, it has been found through simulation that the use of 120 degree antennas provide too much overlap.As the coverage of any sector within aCDMAsystemis directly affected by the noise generated by its neighboring sectors andtrafficwithin those sectors, the use of 120 degree can lead to reduced coverage area through the rise in system noise. The excessive overlap of sectors can also lead to increasedsofterhandoffand therefore the reduction of call processing capability.If narrow horizontal beamwidth antennas are used, for example 60 degrees, simulation has shown that insufficient coverage (i.e. coverage holes) can exist between adjacent sectors. The use of 60 degree high gain antennas can also restrict the vertical beamwidth and can lead to coverage nulls close to the cell site. From current simulation, the optimum horizontal antenna beamwidth for PCS systems has been found to be between 90 and 100 degrees.This beamwidth has been proven to minimize softer hand off while providing adequate coverage. However, before choosing an antenna of this beamwidth, the system engineer should ensure that all factors outlined within this Antenna Parameters subsection have been identified.Voltage Standing Wave Ratio and Return LossVoltage Standing Wave RatioVoltage Standing Wave Ratio (VSWR) is another parameter used to describe anantennaperformance. It deals with the impedance match of the antenna feed point to the feed ortransmissionline. The antenna input impedance establishes a load on the transmission line as well as on the radio link transmitter andreceiver.To have RF energy produced by the transmitter radiated with minimum loss or the energy picked up by the antenna passed to the receiver with minimum loss, the input or base impedance of the antenna must be matched to the characteristics of the transmission line. The VSWR of a PCS antenna should be less than 1.5:1.Return LossReturn loss is the decibeldifference betweenthe power incident upon a mismatched continuity and the power reflected from that discontinuity. Return loss can be related to the reflection coefficient (VSWR) as follows;RLdB = 20 log (1/p) Where p = VSWR-1/VSWR+1VSWR = Vmax/VminIn other words, the return loss of an antenna can be considered as the difference in power in theforwardandreversedirections due to impedance mismatches in the antenna design. All other things being equal, the higher the antenna return loss, the better the antenna.Thesystemengineer should choose an antenna with a return loss of 14 dB or better. Note that 14 dB corresponds to a VSWR of 1.5:1 as per the following example;VSWR = 1.5/1 = 1.5 p = 1.5 VSWR-1/VSWR+1 = 0.5/2.5 = 0.2RLdB = 20log (1/0.2)RLdB = 13.979 dBHow Antenna Downtilting selection for cdma ?Downtilting is the method of effectively adjusting the vertical radiation pattern of theantennato increase the amount ofpowerradiated downwards. Downtilting can be used to increase the amount of coverage close to the site where nulls (holes) may exist due to the effective height of the antenna.Downtilting can also be used to reduce pilotpollution caused by reflections or undesired RF propagation beyond a pre-determined footprint. There are principally two types of antenna downtilting possible, mechanical and electronic.Mechanical downtilting can be achieved through the mechanical adjustment of an antennasphysicalposition. The main advantage of the mechanical type of downtilting is the ease (dependent upon location) of mechanically adjusting the antennas direction followingsystemoptimization.Note that any cellular or PCSnetworkwill require some degree of system optimization based upon site specific variables. The adjustment of antenna downtilt has historically been one of the principle methods of tuning system performance, therefore the system engineer should consider if the chosen antenna can be downtilted and if so, by how much?The second method of downtilting that can used for Cellular/PCS applications is Electronic downtilt. This is the only way to implement downtilt for an Omni directional antenna. The level of electronic downtilt for an antenna is normally pre-set and ordered directly from the antenna manufacturer.The system engineer should be aware that as electrical antenna downtilt is pre-set,the field adjustment of downtilt and therefore vertical radiation can not normally be reduced.The system engineer should also remember that the amount of gain in the antenna will also have a direct affect both on the physical size of the antenna and the vertical beamwidth. If a low gain antenna is utilized, the vertical beamwidth will be relatively broad and therefore the benefits of down tilting will be minimal.Global Positioning System GPSThe Global Positioning System (GPS) is a radio-navigation system that employs RF transmitters in 24 satellites. The satellite configuration when completed will guarantee that a GPSreceiverlocated anywhere on earth can receive RF signals from at least four satellites 24 hours a day (with unobstructed visibility).For commercial use, each satellite transmits unique bi-phase pseudo-random- noise codes on the L-bandcarrierfrequencyof 1.57542 GHz. A GPS receiver decodes the spread-spectrum modulations and uses triangulation techniques on the signals to calculate precise latitude, longitude, altitude and timing information from a position on earth.GPS, officially known as the NAVSTAR GPS (Navigation System with Timing and Ranging Global Positioning System) is operated by the Department of Defense (DoD). It consists of 21 operational satellites and 3 spares circling the earth once every 12 hours.The GPS receiver when used as a synchronization source for a CDMA cell-site, offers several significant advantages over the other alternatives.The system provides world-wide coverage, absolute system time information, excellent accuracy, and all at a relatively low cost. There are however some limitations associated with the use of GPS which prevent it from being the total systemsolutionfor base station synchronization. The requirement for an unobstructed view of the satellite orbits force several restrictions on antenna placement and cabling at a cell-site.Several environmental factors (i.e. snow, sleet, debris, RFinterference) can severely degrade receiver performance. Field tests have shown that some receivers can be jammed by intentional or non-intentional low power interference sources over a fairly wide range (1 Watt up to 14 miles).Since the entirenetworkis under DoDcontroland has important military significance, the uninterrupted availability of the system can also be cause for concern. Selective Availability (SA) can degrade the accuracy of the GPS system for civilian use, by intentionally introducing random jitter into the timing signals being transmitted.For normal levels of SA, the GPS system with proper filtering can still provide acceptable accuracies to satisfy CDMA base station timing requirements. Accuracies of +/- 150 nS without and +/- 400 nS with SA are typical.Vocoder: A Voice Compression in CDMAWhen we talk, we pause between syllables and words.CDMAtakes advantageof these pauses in speech activity.

Analog to digital conversionThe voicesignalis converted to a digital signal using PCM.Variable rate vocoderThe vocoder (Voice Coder) is used to compress the digital signal from the Codec (Code/Decode). The vocoder, used in a CDMAsystem, compresses the voice signal into various data rates. The data rate is dynamically determined by the users speech activity.The vocoders are located at the BSC and in the phone.Vocoder ratesThe voice is compressed in the vocoder into either one of four rates (Full, 1/2, 1/4, or 1/8 rate). CDMA systems can use either an 8 kbps or 13 kbps vocoder.Definition of Forward Channel in CDMAThere are FourchannelinForwarddirection in cdma.1. PILOT CHANNEL (1)2. SYNC CHANNEL (1)3. FORWARDTRAFFIC+PAGINGCHANNELS (62)4. PAGING CHANNELS ( MAXIMUM 7)PILOT CHANNELPILOT SIGNALS ARE TRANSMITTED BY EACH CELL SITE TO ASSIST MOBILE RADIO IN ACQUIRING AND TRACKING THE CELL SITEDOWNLINKSIGNALPILOT CHANNEL IS ASSIGNED CODE CHANNEL NUMBER ZEROTHE SIGNAL STRENGTH OF THE PILOT CHANNELS IS MEASURED BY Ec/IoEc/Io IS THE ENERGY PER CHIP PERINTERFERENCEDENESITY MEASURED ON THE PILOT CHANNELEc/Io EFFECTIVELY DETERMINES THE FORWARD COVERAGE AREA OF A CELL OR A SECTORSYNC CHANNELSYNC CHANNEL IS GIVEN THE CODE CHANNEL NUMBER 32; FIXED DATA RATE 1200 KBPSALLOWS RECIEVER TO OBTAIN FRAME SYNCHRONIZATION ON SIGNALMESSAGES SENT ON SYNCH CHANNEL ARE SYSTEMTIME CHARACTERISTICS OF THE SYSTEMFORWARD TRAFFIC AND PAGING CHANNELSPAGING CHANNELS ARE GIVEN THE CODE CHANNEL NUMBER 1 THRU 7FORWARD TRAFFIC CHANNELS GROUPED INTO RATE SET 1( 9.6, 4.8, 2.4 or 1.2 KBPS) AND RATE SET 2 (14.4, 7.2, 3.6 or 1.8 KBPS)RATE SET 1 IS REQUIRED FOR IS-95 WHEREAS RATE SET 2 IS OPTIONALSPEECH IS ENCODED WITH VARIABLE RATE VOCODER TO GENERATE FORWARD TRAFFIC CHANNEL DATA DEPENDING ON VOICE ACTIVITYWhy Power Control Essential in CDMA ?Power controlis essential for the smooth operation of a cdma system. Because all users share the same rf band through the use of pn codesEach user looks like random noise to other users.The power of each individual user therefore, must be carefully controlled so that no one user is unnecessarily interfering with others who are sharing the same band.Near mobiles must transmit at lower powerThan distant ones to balance linkNeed for powercontrolin a cdma arises because of the near-far problem.

All the handsets in a cdma system transmit and receive on the same radiofrequencySignals form one mobile appear as noise to the other mobileIf two mobiles at different distances form the base station transmit at same power than the mobile which is nearer to the base station increases the noise floor for the mobile which is far from the base stationIn other words if the power of the mobile which is near to the base station is not controlled than it increases interfences at the reciever for the other mobiles which are far from the base station.The mobiles far from the base station in this case have to increase there transmit power to overcome thisinterferencelevelTherefore power control is implemented in cdma system to overcome this near-far problemHandset measures data errors and sends signal quality to bsBs makes minor changes in power level (+- 3 db)Base station measures data errors from handsetBs commands the mobile to increase or decrease powerBY 1 dbPower control occurs 800 times per secondValues for initial power on access ortrafficchannels are sent on overhead message onpagingchannelVocoders and its Type in CDMAVocodersHuman voice is made up of a combination of voiced and unvoiced soundsVocoders exploit these properties of speech production mechanismVocoders do not respond to music, non-human sounds and tones from voice band modemsPCM vs VOCODERS

CDMAVOCODERS8 kbps variable rate coder Rate 1 Rate 1/2 Rate 1/4 Rate 1/8Cdma development group 13.3 kbps VOCODER8 kbps enhanced rate variable coder (evrc)EVRC ( Enhanced Variable Rate Coder )It is an 8 kbps vocoder thats supposed to sound about as good as the current 13 kbps vocoder. Thus, you can have the same voice quality while improving the capacity of thesystemEvrc uses a adaptive noise cancellation filter prior to encoding which ensures that noise never reaches the encoder which is tightly optimized for speech giving high quality voice at low bit rates.What is RAKE RECEIVER and its Purpose in CDMARakeReceiverInstead of trying to overpower or correct multipath problems, CDMA takes advantage of the multipath to improve reception quality in fading conditions. CDMA does this by using multiple correlating receivers and assigning them to the strongest signals. This is possible because the CDMA mobile is synchronized to the serving base station. The mobiles receiver can distinguish direct signals from multipath signals because the reflected multipaths signals arrive later than the direct signals.

Special circuits called searchers are also used to look for alternate multipaths and for neighboring base station signals. The searchers slide around in time until they find a strong correlation with their assigned code. Once a strongsignalis located at a particular time offset, the searcher assigns a receiver element to demodulate that signal. The mobile receiver uses three receiving elements, and the base station uses four. This multiple correlatorsystemis called a rake receiver. As conditions change the searchers rapidly reassign the rake receivers to handle new reception conditions.Instead of trying to overpower or correct multipath problems, CDMA takes advantage of the multipath to improve reception quality in fading conditions. CDMA does this by using multiple correlating receivers and assigning them to the strongest signals. This is possible because the CDMA mobile is synchronized to the serving base station. The mobiles receiver can distinguish direct signals from multipath signals because the reflected multipaths signals arrive later than the direct signals.Special circuits called searchers are also used to look for alternate multipaths and for neighboring base station signals. The searchers slide around in time until they find a strong correlation with their assigned code. Once a strong signal is located at a particular time offset, the searcher assigns a receiver element to demodulate that signal. The mobile receiver uses three receiving elements, and the base station uses four. This multiple correlator system is called a rake receiver. As conditions change the searchers rapidly reassign the rake receivers to handle new reception conditions.Rake Receiver DesignThe design of a rake receiver can be visualized as a series of time delayed correlator taps fed from a commonantenna. If each correlator tap is delayed to match the arrival of a particular transmitted signal, then the outputs of each tap can be recombined in phase. Once an RF signal with a particular travel time is locked onto by the correlator tap, an estimate of the gain or loss experienced by that signal must be made. The weighting of the taps perform this gain normalization function. Once adjusted, the outputs of each finger of the rake can be combined to form a better version of the transmitted signal. Notice that this description visually matches the analogy of a common garden rake with each tap forming a tine of the rake, hence the name rake receiver.Another form of timediversityoccurs in the base station when transmitting at reduced data rates. When transmitting at a reduced data rate (more detail will be presented on this later), the base station repeats the data resulting in full ratetransmission. The base station also reduces the transmitted power when it operates at reduced data rates. This added redundancy in the transmitted signal results in lessinterference(power is lowered) and improves the CDMA mobiles station receiver performance during high levels of interference.

CDMA Spatial DiversityDiversityReception:Multiple Antennas at Base Station EachAntennais Affected by Multipath Differently Due to Their Different Location Allows Selection of theSignalLeast Affected by Multipath FadingIf Diversity Antennas are Good, Why Not Use Base Stations as a DiversityNetwork? SoftHandoffThe concept of diversity reception has been well known for some time. A diversityreceiveruses multiple antennas at one reception site. Since these antenna are placed to be a non-integral number of wavelength apart, when one antenna is experiencing a multipath fade it is likely that the other antennas will not be in a fading condition.This leads to receiver designs where the antenna with the best signal is selected to be processed by the receiver. AMPS analog cellular base stations use this type of diversity for improved fading resistance. CDMA also employs diversity reception for base stations.One of the most problematic locations for a cellular phone is in between cells where handoffs occur. If the mobile experiences a deep fade during handoff, a dropped call can result.If diversity reception is useful at a single receiver location, then can using multiple base station be used in a diversity network to help phone during handoffs? The answer is yes: CDMA seeks to overcome the handoff problem by using two or three base stations as a giant diversitysystem.Using multiple base stations simultaneously talk to the mobile during a handoff is known as a soft handoff.How Spatial Diversity works during Soft Handoff in CDMA ?CDMA extends the idea ofdiversityreception with the concept of softhandoff. In the slide, a mobile CDMA phone has established a call with base station one. As the mobile moves away from base station one and approaches base station two, a device in the phone known as the searcher identifies base station one as a good candidate for soft handoff.

The searcher identifies other base stations as good candidates for soft handoff when the received level exceeds the T_add (Threshold for adding a candidate cell for soft handoff) parameter of thesystem. Once a candidate exceeds the threshold, the phone sends the candidate information to the Mobile Telephone Switching Office (MTSO) via base station one. If thenetworkhas available capacity, the MTSO then directs the base stations and mobile to perform a soft handoff.During soft handoff, the mobile listens to the two cells on different codes while the base stations each listen to the sametransmissionfrom the mobile. The signals from the base to mobile are treated as multipath signals and are coherently combined at the mobile unit.Each base station sends its received signal via the network to the (MTSO), where a quality decision is made on a frame-by-frame basis, every 20 msec. The MTSO selects the better frame from the two signals returned from the base stations. Thus the two base stations act like a giantantennadiversity system. This helps to overcome the fading problem that occurs between cells where handoffs must take place.As the mobile moves further away from base station one, the searcher in the phone will determine that its power has dropped below the system parameter T_drop. The T_drop information is sent to the MTSO, which then directs the soft handoff be terminated.This allows for smooth handoffs between cells that the user is totally unaware of. Of course there is a price to pay for this clever design: the system uses more capacity for each soft handoff made and there is greatly increased networktrafficbetween CDMA cellsites and the MTSO.

How Frequency Diversity works in CDMA?Frequencydiversityis inherent in a spread spectrumsystem. A fade of the entiresignalis less likely than with narrow band systems.

Combats Fading, Caused by Multipath Fading Acts like Notch Filter to a Wide Spectrum Signal May Notch only Part of SignalFading is caused by reflected images of an RF signal arriving at thereceiversuch that the phase of the delayed (reflected) signal is 180 degrees out of phase with the direct RF signal.Since the direct signal and delayed signal are out of phase, they cancel each other causing the amplitude seen by the receiver to be greatly reduced. In the frequency domain, a fade appears as a notch filter that moves across a band. As the user moves, the frequency of the notch changes.The width of the notch is on the order of one over the difference in arrival time of two signals. For a 1 usec delay, the notch will be approximately 1 MHz wide. The TIA CDMA system uses a 1.25 MHzbandwidth, so only those multipaths of time less than 1 usec actually cause the signal to experience a deep fade. In many environments, the multipath signals will arrive at the receiver after a much longer delay.This means that only a narrow portion of the signal is lost. In the display shown, the fade is 200 to 300 kHz wide. This results in the complete loss of an analog or TDMA signal but only reduces the power in a portion of a CDMA signal. As the spreading width of a CDMA signal increases, so does its multipath fading resistance. Many spread spectrum systems use a 5 or 10 MHz widechannelto further improve fading resistance.What is Correlation in CDMA ?Correlation Is a Measure of How Well a GivenSignalMatches a DesiredCode, The Desired Code is Compared to the Given Signal at Various Test times.

Correlation is key enabling concept for direct sequenceCDMAsystems. Correlation is a measure of how well a given signal spread with a digital code matches a desired code. In the above example, a digital sequence is received and then compared to the desired code.This comparison takes place over a range of different times. When time aligned, the correlation is 1 indicating that an exact match occurred between the received signal and the desired signal.At other times the correlation is near zero, especially if the digital codes used to spread the waveform are designed properly. It is the fact that we can correlate to signals that enables direct spread CDMA to function.What is CDMA Time Diversity ?Timediversityis a technique common to most digitaltransmissionsystems. The RakeReceiveris used to find and demodulate multipath signals that are time delayed from the mainsignal.Rake Receiver to Find and Demodulate Multipath Signals.Data is Interleaved :Spreads Adjacent Data in time to Improve Error Correction EfficiencyConvolutional Encoding :Adds Error Correction and DetectionViterbi Decoding :Most Likely Path Decoder for Convolutionaly Encoded DataTransmitted signals are spread in time by use ofinterleaving. Interleaving the data improves the performance of the error correction by spreading errors over time. Errors in the real world duringradiotransmission usually occur in clumps, so when the data is de-interleaved, the errors are spread over a greater period of time. This allows the error correction to fix the resulting smaller, spread out errors.Forwarderror correction is also applied to the transmitted data. This is usually done by adding parity bits that allow received errors to be detected and to some extent corrected. Performance of the receiver can be further enhanced by using a maximal likelihood detector. The particular scheme used for CDMA is convolutional encoding in the transmitter with Viterbi decoding using soft decision points in the receiver.

How Interleaving Improves Data Transmission Systems?

This graphically demonstrates whyinterleavingdata improves error correction performance of datatransmissionsystems. In the top Image, data is sequentially read out of a buffer than goes by rows. No interleaving is employed. The data is read and transmitted in numerical order.During transmission, data blocks 5 through 8 are corrupted by someinterference. When the data is received, blocks 5 through 8 are lost and the error correction is insufficient to recover such a large block of lost data.In the lower image, the same data is first interleaved using a simple pattern of reading the rows into columns. The interleaved data is then read out by row and transmitted. During transmission the data in the same four blocks is corrupted by interference.However, the blocks that were lost are no longer sequential. Blocks 2, 6, 10, and 14 were lost. When the interleavedsignalis received, thereceiverreverses the interleaving process to restore the data to its original sequential pattern.Notice what happens after de-interleaving: the lost blocks are now spread in time resulting in small, isolated error locations. Now the limited error correction built into the signal can correct the errors. Interleaving makes the most use of the error correction built into a data transmissionsystem.

How Power Control in Reverse Link in CDMA ?Power ControlRequired inReverselink cdma due to following reason.Maximum System Capacity is Achieved if: All Mobiles are Power Controlled to the Minimum Power for Acceptable Signal Quality As a Result, all Mobiles are Received at About Equal Power at the Base Station Independent of Their LocationTwo Types ofControl Open Loop Power Control Closed Loop Power ControlOpen & Closed Loop Power Control are Always Both ActiveOne of the fundamental enabling technologies of CDMA is power control. Since the limiting factor for CDMA system capacity is the totalinterference, controlling the power of each mobile is critical to achieve maximum capacity. CDMA mobiles are power controlled to the minimum power that provides acceptable quality for the given conditions.As a result, each mobiles signal arrives at the base station at approximately equal levels. In this way, the interference from one unit to another is held to a minimum. Two forms of power control are used for the reverse link: open loop power control, and closed loop power control.Despite what seemslogical, both open and closed loop power control are active at the same time once atrafficchannelis established. Both are constantly active and controlling the power of the phone according to their respective control algorithms.

Open Loop Power Control in CDMAThe Open LoopPower Controlrequire in cdma due to following reason. Assumes Loss is Similar onForwardandReversePaths Receive Power + Transmit Power = -731. All Powers in dBm Example: For a Received Power of -85 dBm1. Transmit Power = (-73) (- 85)2. Transmit Power = +12 dBm Provides an Estimate of Reverse TX Power for Given Propagation ConditionsOpen loop powercontrolis based on the similarity of the loss in the forward path to the loss in the reverse path (forward refers to the base-to-mobile link, while reverse refers to the mobile-to-base link).Open loop control sets the sum of transmit power and receive power to a constant, nominally -73, if both powers are in dBm. A reduction in signal level at the receive antenna will result in an increase in signal power from the transmitter.For example, assume the received power from the base station is -85 dBm. This is the total energy received in the 1.23 MHzreceiverbandwidth. It includes the composite signal from the serving base station as well as from other nearby base stations on the samefrequency.The open loop transmit power setting for a received power of -85 dBm would be +12 dBm. Thus open loop power control adjusts the transmit power of the phone to match the propagation conditions that the phone is experiencing at any given time.By the TIA/EIA-98 standard specification, the open loop power control slew rate is limited to roughly match the slew rate of closed loop power control directed by the base station. This eliminates the possibility of open loop power control suddenly transmitting excessive power in response to a receiver signal level dropout.Why Closed Loop Power Control in CDMAClosed looppower controlis used to allow thepowerfrom the mobile unit to deviate from the nominal as set by open loopcontrol. This is done with a form of delta modulator. The base station monitors the power received from each mobile station and commands the mobile to either raise power or lower power by afixedstep of 1 dB. This process is repeated 800 times per second, or every 1.25 msec.The power control data sent to the mobile from the base station is added to the data stream by replacing the encoded voice data. This processes in called puncturing, since the power control data is written into the data stream by over writing the encoded voice data. The power control data occupies 103.6 micro-seconds of each 1.25 milli-second of data transmitted by the base station.Because the mobiles power is controlled to be no more than is needed to maintain the link at the base station, a CDMA mobile typically transmits much less power than an analog phone.The base station monitors the receivedsignalquality 800 times per second and directs the mobile to raise or lower its power until the received signal quality is just adequate. This operating point varies with propagation conditions, the number of users, and the density and loading of the surrounding cells.Analog cellular phones need to transmit enough power to maintain a link even in the presence of a fade. Most of the time, analog phones transmit excess power. CDMA radios are controlled in real time and kept at a power level to just maintain a qualitytransmissionbased on the changing RF environment.This has the benefit of longer battery life and smaller, lower cost amplifier design. If recent health concerns over cellular phone radiation are determined to have some basis in fact, CDMA will be preferred because of its much lower RF output power.What Closed Power Control Criteria ? Directed by Base Station Updated Every 1.25 msec Commands Mobile to Change TX Power in +/- 1 dB Step Size Fine Tunes Open Loop Power Estimate Power Control Bits are Punctured over the Encoded Voice Data Puncture Period is Two 19.2 kbps SymbolPeriods = 104.2 usec