A. Noncoherent Orthogonal Modulation
Scheme. For a binary signaling scheme that involves the use of two signals
Tttsts ≤≤0),(),( 21
which are orthogonal with equal energy,
let Tttgtg ≤≤0),(),( 21
denote the phase-shifted version of , res. , which remain orthogonal and of equal energy. This scheme is referred to as noncoherent orthogonal modulation.
)(),( 21 tsts
3. Noncoherent Binary Modulation Techniques3. Noncoherent Binary Modulation Techniques
A digital communication receiver with no provision make for carrier phase recovery is said to be noncoherent.
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At the receiver, the received signal x(t) can be expressed as follows
⎩⎨⎧
≤≤+≤≤+
=TttstntgTttstntg
tx0 sent, )( ),()(
0 sent, )( ),()()(
22
11
The receiver tries to discriminate between s1(t) and s2(t), regardless of the carrier phase. This goal can be achieved by the following receiver structure:
)(tx Comparisondevice
1l
⎪⎪⎩
⎪⎪⎨
⎧
<
>
)( choose If
)( choose If
2
21
1
21
tsll
tsll
Figure 1. Binary receiver for noncoherent orthogonal modulation
Matchedto φ1(t)
Envelopedetector
2lMatchedto φ2(t)
Envelopedetector
Sample at t = T
Sample at t = T
An noncoherent matched filter may be viewed as being equivalent to a quadrature receiver, as illustrated below. The quadrature receiver itself has two channel (recall that QPSK receiver).
)(tx
×
)(tiφ
∫T
dt0
× ∫T
dt0
+ Squarerooter
2il
Let φ1(t) and φ2(t) be the orthonormal set of s1(t) and s2(t) and be the version of that results from shifting the carrier phase by -90 degrees . The quadrature receiver is shown in Figure 2 where i = 1, 2.
In-phase channel
Qradrature channel
)(~ tiφ
)(tiφ
Square-law
device
Square-law
device
2Iix
2Qix
Figure 2)(~ tiφ
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Remark. The average probability of error for the noncoherent receiver, Figure 1, or equivalently Figure 2, is given by a simple formula
⎟⎟⎠
⎞⎜⎜⎝
⎛−=
02exp
21
NEPe
where E is the signal energy per symbol and N0/2 is the noise spectral density. We list this result here without proof. The proof can be found the text book.
(1)
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B. Noncoherent BFSK
For the binary FSK case, the transmitted signal is
2,1 0 ),2cos(2)( =≤≤= iTttfTEts bib
bi π 2,1 ,integer , ==
+= in
Tinf c
b
ci
i.e.,22
11
frequency using)(0 frequency using )(1
ftsfts
↔↔
Thus the noncoherent binary FSK is a special case of noncoherentorthogonal modulation with and , where Tb is the bit duration and Eb is the signal energy per bit. From (1), we have the average probability of error (bit error rate) for noncoherent BFSK is
bTT = bEE =
⎟⎟⎠
⎞⎜⎜⎝
⎛−=
02exp
21
NEP b
e
)(txComparison
device
1l
⎪⎪⎩
⎪⎪⎨
⎧
<
>
0 choose If
1 choose If
21
21
ll
ll
Figure 3. Noncoherent receiver for BFSK
Matched to Envelopedetector
2lEnvelopedetector
Sample at t = Tb
Sample at t = Tb
tfTb 12cos/2 π
bTt ≤≤0
Remark. When comparing the error performance of noncoherent FSK with coherent PSK, it is seen that for the same Pe, noncoherent FSK requires approximately 1 dB more Eb/N0 than does BFSK (for ) , because coherent reference signals need not be generated. Therefore, almost all FSK receivers use noncoherent detection. In the following, we will see that the same phenomenon occurs for noncoherent DPSK and PSK.
410−≤eP
Matched to tfTb 22cos/2 π
bTt ≤≤0
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C. Differential Phase-shift Keying (DPSK)
Transmitter’s two operations: (1) differential encoding of the input binary sequence and(2) phase-shift keying
Generation of DPSK:
For an input binary sequence , a differential encoded sequence is determined by
kkk bdd ⊕= −1 or kkk bdd ⊕= −1
where ⊕ denotes the modulo 2 operation and the overbardenotes complement.
}{ kb}{ kd
}{ kb 1 1 0 1 0 1 1 0 0 1
Table 1. Illustrating the generation of DPSK signal
index k: 0 1 2 3 4 5 6 7 8 9 10
Differentially encoded sequence
}{ kd ref. bit 1 1 1 0 0 1 1 1 0 1 1 kkk bdd ⊕= −1
Corresponding phase shift
)}({ kθ π π 0 0 π π π 0 π π
Remark. DPSK is an another example of noncoherent orthogonal modulation, when it is considered over two bit intervals. In this case, from (1) we get the average probability of error for DPSK is
⎟⎟⎠
⎞⎜⎜⎝
⎛−=
0
exp21
NEP b
e
since T = 2Tb and E = 2Eb.
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Remark. When comparing the error performance of (2) with that of coherent PSK, it is seen that for the same Pe, DPSK requires approximately 1 dB more Eb/N0 than does BPSK (for ). It is easier to implement a DPSK system than a PSK system, since the DPSK receiver does not need phase synchronization.
410−≤eP
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Error Probability of M-ary Digital PAM SignalsSignal Representation of M-ary PSKSignal Representation of M-ary FSK
4. M-ary Modulation Techniques4. M-ary Modulation Techniques
Quaternary case:
,)2/3()(1 ats −= ,)2/1()(2 ats −=
,)2/1()(3 ats = ,)2/3()( and 4 ats =
Tt ≤≤0for
)(1 tφZ3
Z1 Z4Z2
Tas23
11 −= Tas21
21 −= Tas21
31= Tas23
41=
Ta− Ta0
m1 = 00 m2 = 01 m3 = 11 m4 = 10
Signal Constellation of Quaternary Signaling Scheme under Gray Code
⎟⎟⎠
⎞⎜⎜⎝
⎛=
0243
NTaerfcPe
where is the minimum distance of the polar quaternary signal constellation.
⎟⎟⎠
⎞⎜⎜⎝
⎛=
0243
Nderfc
Tad =
A. Error Probability of M-ary Digital PAM Signals
)(1 tφ
Z1
000
ds27
11 −=
Tad =
ds21
51 = ds23
61 =
d0
⎟⎟⎠
⎞⎜⎜⎝
⎛==
0221)111()000(
NderfcPP ee
Try for M = 8, which has the signal constellation as below (Gray code). Show that
Z2
001
Z3
011
Z4
010
Z5
110
Z6
111
Z7
101
Z8
100
(1) (2)⎟⎟⎠
⎞⎜⎜⎝
⎛==
02)011()001(
NderfcPP ee
ds25
21 −= ds23
31 −= ds21
41 −= ds25
71 = ds27
81 =0
d2−d3− d− d2 d3
where which is the minimum distance of the above signal constellation.
In general, for M-ary PAM, if the signal points are
then
12111 ,,, Msss L
dMdddddM2
1,,23,
21,
21,
23,,
21 −
−−−
− LL
⎟⎟⎠
⎞⎜⎜⎝
⎛−=
021
Nderfc
MMPe
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Tnf cc /=
Tt,...,MiM
itfTE
ts ci ≤≤=−
+= 0 ,1 ),)12(2cos(2
)( ππ
B. M-ary PSK Scheme:
The phase of carrier takes on one of M possible values, namely,
MiMii ,...,1 ,/)12( =−= πθ
A M-ary signal set is represented as
where T is the symbol duration and E is the signal energy per symbol. The carrier frequency where nc is a fixed integer.
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Thus, the signal constellation of M-ary PSK is two-dimensional. The M messages are equally spaced one circle of radius and center at the origin, see Figure 1 for an example of octa-PSK.
Figure 1. Signal Constellation for octa-PSK (M = 8). The decision boundaries are shown as dashed lines.
Similar as we did for QPSK, each signal si(t) can be represented by the following two orthogonal functions with unit energy:
)2sin(2)( and )2cos(2)( 21 tfT
ttfT
t cc πφπφ ==
M/π
M/π
is
Remark. The probability of correct reception is to integrate the shaded area. This probability can be bounded by some bound. Therefore, for large values of E/N0, the probability of symbol error is approximately given by
4
,sin20
,
≥
⎟⎟⎠
⎞⎜⎜⎝
⎛≈−
M
MNEQP PSKMe
π
The coordinates of the received signal given si(t) was transmitted is
where nI and nQ are Gaussian random variables with zero mean and variance N0/2 (why ?).
,)12(cos II nM
iEx +⎟⎠⎞
⎜⎝⎛ −
=π Min
MiEx QQ ,...,1 ,)12(cos =+⎟
⎠⎞
⎜⎝⎛ −
−=π
(A)
C. M-ary FSK
In an M-ary FSK scheme, the transmitted signals are defined by
MiTttfifTEtsi ,..,1,0 ,])1([2cos2)( 0 =≤≤Δ−+= π
where is taken as an integer for convenience and is the minimum frequency spacing such that adjacent signals are orthogonal (recall this result form MSK).
Tf0 )2/(1)( min Tf =Δ
For coherent M-ary FSK, the optimum receiver consists of a bank of M correlations or matched filters. At the sampling times t = kT, the receiver makes decisions based on the largest matched filter output. The probability of symbol error can be upper bounded by
⎟⎟⎠
⎞⎜⎜⎝
⎛−≤−
0, )1(
NEQMP FSKMe
where is the energy per symbol and M is the size of the symbol set.
)(log2 MEE b=
(B)
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5. Multi-carrier Modulation and OFDM5. Multi-carrier Modulation and OFDM
Applications of M-ary FSK: multicarrier modulation and OFDMGoal: for combating ISI
Multicarrier modulation is a way to transmit digital data through bandlimited channel. Design of a bandwidth-efficient communication system in the presence of channel distortion or equivalently ISI, is to divide the available channel bandwidth into a number of equal-bandwidth subchannels, where the bandwidth of each channel is sufficiently narrow so that the frequency response characteristics of the subchannels are nearly equal. Such a division of the overall bandwidth into smaller subchannels is illustrated in Figure 1.
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Number of Subchannels: Then data symbol is transmitted by frequency-division multiplexing (FDM). This is known as a multicarriermodulation system. Orthogonality: Each subchannel is associated a carrier fi, where
which is the mid-frequency in the ith subchannel. If the subcarriers are orthogonal over the symbol duration T, then it is referred to as orthogonal frequency-division multiplexing (OFDM). Thus OFDM is a special case of multicarrier modulation.
Nififfi ,,1 ,)1(0 L=Δ−+=
Description:
fWN Δ= /
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ISI Reduction: the subcarriers are spaced by 1/Ts Hz, where Ts is the symbol duration of the subcarriers, then Tofdm, the symbol duration of the OFDM system is related by
By selecting N to be sufficiently large, the symbol interval Ts of the subcarriers can be made significantly larger than the time duration of the channel-time dispersion. Hence, ISI can be made arbitrarily small by selection of N. In other words, each subchannel appears to have a fixed frequency response C(fk), k = 0, 1, … , N - 1.
Description (Cont.):
ofdms NTT =
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OFDM Implemented by IDFT and DFT
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Disadvantage: A major problem with the multicarrier modulation in general and OFDM system in particular is the high peak-to-averagepower ratio (PAR) that is inherent in the transmitted signal.
Applications: High-speed transmission over telephone lines, such as digital subcarrier lines. This type of OFDM modulator has also been called discrete multitone (DMT) modulator. OFDM is also used indigital audio broadcasting in Europe and other parts of the worldand in digital cellular communication systems.
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A. Bit Error Probabilities from Symbol Error Probabilities
There are two approaches to define an equivalent bit error probability, Pb, or bit error rate (BER), from a symbol error probability, Ps. It depends on
(1) structure of the signal space, and(2) the mapping of the signal space points into equivalent
bit sequences.
6. Comparison of Digital Modulation Systems6. Comparison of Digital Modulation Systems
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Definition 1. We assume that in going from one signal point to an adjacent signal point, only one bit in the binary word representing the signal changes. In this case,
MPP s
b2log
=
Remark. M-ary PSK, if a Gray code is employed and M-ary QAM are of the case.
In the following, we will give an explicit formula for Pb. Notice that
Definition 2. Denote . We assume that all symbol errors are equally likely. We define as theratio of A, the average number of bit errors per n-bit symbols to n, number of bits per symbol.
bP
Mn 2log=
)1( −MP s
- Each symbol is in error in an M-ary system with probability
)1(1
1 −⎟⎟⎠
⎞⎜⎜⎝
⎛== ∑
= MP
kn
knn
AP sn
kb
- For a given symbol error, suppose that k bits are in error.
There are ways that this can happen, which results⎟⎟⎠
⎞⎜⎜⎝
⎛kn
sPM
M)1(2 −
= 2/sP→
for large M.
Remark. M-ary FSK is of this case.
B. Bandwidth Efficiencies of M-ary Digital Comm. Systems (DCS)
Goal: Consider the bandwidth efficiencies in terms of bits per second per hertz (bps/Hz) of bandwidth of various digital modulation schemes.
For a M-ary DCS, let Rb denote the bit rate and Rs symbol rate. Then
sb RMR )(log 2=
For a M-ary PSK, QAM, DPSK, the null to null bandwidth is
MRB b
XM2
, log2
= (bps/Hz) )(log5.0 2,
MB
R
XM
b ==⇒ ρ
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For a M-ary FSK, consider the spacing between frequency is minimum. Then the bandwidth is
MRMB b
MFSKcoh2
, log2)3( +
=
Table 1. Bandwidth Efficiencies of M-ary Signals
M 2 4 8 16 32 64
2.5 3
.1875.3125
ρ: PSKDPSKQAM
0.5 1 1.5 2
ρ : FSK 1 1 .75 .5
(bps/Hz) 3
log2 2
, +==⇒
MM
BR
MFSKcoh
bρ
Remark:
(1) M-ary PSK and M-ary QAM have 2-dimensional signal space and they are both bandwidth efficient (or called spectral efficient).
(2) MFSK has M-dimensional signal space and it is bandwidth inefficient.
Note. The other parameter used in comparing performance (power efficiencies) of different schemes is E/N0, the ratio of symbol energy to noise power spectral density. In other words, it is to make comparisons between different DSCs on the basis of the relative signal power needed to support a given received information rate assuming identical noise environment.
510 −=eP
)dB(/ 0NE b
R = C
2
4
8
16
8 0-.1-1.6 6 12 1 24 3-2
M-PSK
4
16
2
WR b /=ρ
16 M-QAM
1
1/2
M=24
816
M-FSK
Power limited region
Bandwidth limited region
R < CR > C
Figure 1. Band Width Efficiency Plane
C = W log2(1 + P/WN0)bits/s
Shannon’s system capacity C of an AWGN channel:
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7. Synchronization7. Synchronization
Synchronization at three levels:
A. Carrier synchronization (or called carrier recovery): for estimation of carrier phase and frequency.
When the coherent detection is used, the knowledge of both the frequency and phase of the carrier is necessary. In other words, there has to be phase concurrence between the incoming carrier and a replica of it in the receiver. This is achieved by employing a phase-locked loop (PLL). The following figure shows a block diagram for carrier synchronization for M-ary PSK.
Received M-ary PSKsignal
Mthpower-law BPF × LPF
VCO
Frequency divide by M
Phase-locked loop
To data demodulator/detector
If M = 2, this loop is called a squaring loop.
Figure 1. Mth Power Loop
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B. Symbol Synchronization (or called clock recovery)
The receiver has to know the instant of time at which the modulation can change its state., i.e., the starting and finishing times of the individual symbols, so that it may determine when to sample and when to quench the product integrator. The estimation of these times is called symbol synchronization or clock recovery.
Note. There are typically a very large number of carrier cycles per symbol period, this second level of synchronization is much coarser than phase synchronization (PS), and is usually done with different circuitry than that used for PS.
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One of methods that can achieve this goal is to employ a closed-loop symbol synchronizer. Among the class of closed-loop symbol synchronizers, the early/late-gate synchronizer is the most popular one which shown in Figure 3.
TT 0Δ−
(a) Rectangular pulse g(t)
t
g(t)
a
0 T T TT 0Δ+ 2T0
Ta2
(b) Output of filter matched to g(t)
Figure 2.
∫T
ddt
+
Absolutevalue
∫−dT
dt0
Absolutevalue
VCO F(ω)
|| 1y
|| 2y
|||| 12 yye −=
1y
2y
Loopfilter
Late gate
Early gate
timing
Td 0Δ=
Figure 3. Early/late-gate data synchronizer
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C. Frame Synchronization
Almost all digital data steams have some sort of frame structure. This is to say that the data stream is organized into uniformly sized groups of bits.
For a receiver to make sense of the incoming data stream, the receive needs to be synchronized with the data streams’frame structure. This is called frame synchronization. This is usually accomplished with the aid of some special signaling procedure from the transmitter.
The simplest frame synchronization aid is the frame marker, for example, in T1 system, for a total of 193 bit, one bit is to used as the frame marker.
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The frame marker could be a single bit, or a short pattern of bits that the transmitter injects periodically into the data stream. The receiver must know the pattern and the injection interval. See Figure 4.
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n bits
…
n bits
…
K bits K bits
Data stream
n bits K bits n bits K bits
Receiver generated frame marker replica
Figure 4. Frame marker illustration
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The receiver, having achieved symbol synchronization, correlated the known pattern with the incoming data stream at the known injection interval. If the receiver is not in synchronization with the framing pattern, the accumulated correlation will be low, otherwise, it should be nearly perfect, blemished only by an occasional detection error.
A good synchronization codeword is one that has the property that the absolute value of its “correlation sidelobes” is small. The bit sequences with the property that their largest sidelobe has a magnitude of unity are known as Barker sequences. Unfortunately, the Barker sequences only exist for the length less than 13.
8. Applications to Digital Cellular Communication Systems
In this section, we will present an overview of two types of digital cellular communications systems that are currently in use. One is the GSM ( Global System for Mobile Communication) systems that is widely used in Europe and other parts of the world. It employs time-division multiple access (TDMA) to accommodate multiple users. The second is the CDMA system based on Interim Standard 95 (IS-95) that is widely used in North America and some countries in the Far East.
Remark. The extended versions of GSM and IS-95 are UMTS (Universal Mobile Telecommunications Systems, 1998 or W-CDMA) and CDMA 2000, respectively.
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Generation 1G 2G 2.5G 3G 4/5G
Time Frame 1980s 1990s Late 1990s 2000s(2010 full deployment)
2010s
Signal Type Analog Digital Digital Digital Digital
Multiple Access
FDMA/FDD TDMA/FDDCDMA/FDD
EDGE, GPRS CDMA, W-CDMA, TD-SCDMA
MC-CDMA, OFDM
Frequency spectrum
824-894 MHz890-960 MHz1850-1990 MHz (PCS)
1800-2400 MHz (varies country to country)
Higher-frequency bands 2-8 GHz
Bandwidth 5-20 MHz ≥ 100 MHz
Antenna Optimized antenna, multiband adapter
Smarter antenna, Multiband and wide-band support
FEC Convolutionalrate, 1/2, 1/3
Concatenated coding scheme
Media type Voice Mostly voiceLow-speed data services via modem (10-70 kbps)
Mostly voiceHigher-speed data (10-384 kbps)
Voice High-speed data (144kbps-2Mbps)
Converged voice/data/mutimediaover IP; Ultra-high-speed data (2-100 Mbps)
Evolution of Mobile Communications Systems
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Generation 1G 2G 2.5G 3G 4/5G
Network type
Celluar Celluar Celluar WWANCell based
Integrated WWAN, WMAN, WLAN (Wi-Fi, Bluetooth) and WPAN (Bluetooth)
Structure Infrastructure based
Infrastructure based
Infrastructure based
Infrastructure based network
Hybrid of Infrastructure based and ad hoc network
Switching Circuit switched
Circuit switched Circuit switched
Circuit switchedAnd packet switched
Packet switched
IP support N/A N/A N/A Use several air link protocols, including IP5.0
All IP based (IP6.0)
New applications
Emails, maps/directions, News, shopping, e-commerce, interactive gaming, etc.
Ubiquitous computing with location intelligence
Security M-sequences for voice enc
A5, m-sequences in CDMA, authentication symmetric crypto
A5, m-seq. auth.
Stream cipher, block cipher, symmetric key auth
Public key crypto
Ex system AMPS, NMT, TACS
GSM, DCS1900, IS-95,CdmaOne
GPRS, EDGE
UMTS, IMT200, CDMA2000, WCDMA
×
RPE-LPC
speech coder
analogspeech
13 kbpsChannel
coder
Blockinter-leaver
22.8kbps
Burstassembler
andencryption
TDMAmultiplexer
GMSKmodulator
Frequencyhopping
synthesizer
Channelmeasurement
bits
7 otherusers
…270.8kbps To
transmitter
(a) Modulator PN codegenerator
Frequencysynthesizer
Receivedsignal
PN codegenerator
LPF and A/O
converterBuffer Matched
filterChannelequalizer
Decryptionand
deinterleavingChanneldecoder
Speechsynthesis
(b) Demodulator
Functional block diagram of modulator and demodulator for GSM
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Summary of Parameters in GSM System
System Parameters Specification
Uplink frequency band 890-915 MHz
Downlink frequency band 935-960 MHz
Number of carriers/band 125
Multiple-access method TDMA
Number of users/carrier 8
Date rate/carrier 270.8 Kbps
Speech-coding rate 13 KHz
Speech encoder RPE-LPC
Coded-speech rate 22.8 kbps
Modulation GMSK with BT = 0.30
Interleaver Block
Frequency-hopping rate 217 hops/sec
Multiple Access Methods
The CDMA Cocktail Party
This is great stuff
Where is she
How long will this take
You know thatWhere is the meeting
Who called
Can I go home?How can I get there
Where is the office
Who knows
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Multiple users share a common channel simultaneously by using different codesNarrowband user information is spread into a much wider spectrumby the spreading codeThe signal from other users will be seen as a background noise: multiple access interference (MAI)The limit of the maximum number of users in the system is determined by interference due to multiple access and multipathfading: Adding one user to CDMA system will only cause graceful degradation of quality
Theoretically, no fixed maximum number of users !
Code Division Multiplexing Access (CDMA)Code Division Multiplexing Access (CDMA)
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Despread signal PSD for user 1
Bandwidth
Received signal PSD
Bandwidthuser 1 user 2 user 3 user 4
user M
user 2 user 3 user 4
user M
user 1
signal power
Interferencepower
CDMA is an interference-limitedmultiple access scheme
Despreading
The signal from other users will be seen as a background noise: Multiple access interference (MAI)
Code Division Multiplexing Access (CDMA) (Cont.)Code Division Multiplexing Access (CDMA) (Cont.)
CDMA System Design
VOCODER
1 0 1 0 0 1 CODEC
Voice Coding
Voice Coding
Power Control
9600 bps 4800 bps 2400 bps 1200 bps
Convolutional Encoder and Repetition
Block Interleaver
Wt
1.2288 Mcps
I PN
QPN
1.2288 Mcps
Decimator
MU
X
DecimatorLong
Code PN Generator
User Address Mask (ESN)
19.2 ksps
19.2 ksps
800 Hz
4
Power Control
BitR = 1/2
Forward Link Generation
1 0 1 0 0 1 CODEC
9600 bps 4800 bps 2400 bps 1200 bps
User Address Mask
Convolutional Encoder and Repetition
Block Interleaver
Long Code PN Generator
28.8 ksps
28.8 ksps Walsh
Cover
307.2 kHz
R = 1/3
Data Burst Randomizer
1.2288 Mcps
I PN
QPN
1/2 PN Chip Dela
D1.2288 Mcps
Mobile
Cell
Reverse Link Generation
The CDMA Rate FamiliesIS-95 defines the 9600 bps family of rates (Rate Set 1)
9600, 4800, 2400, and 1200 bpsCan select one of the four rates every 20 ms frame
14400 bps family of rates (Rate Set 2)14400, 7200, 3600, and 1800 bpsCan select one of the four rates every 20 ms frame
Extended rates (extended Rate Set 1)Adds 19200, 38400, and 76800 bpsAt most four rates can be activeCan select one of the four active rates every 20 ms frame
Variable-Rate Vocoder
Encoder
Decoder
64 kbps
PCM
Full Rate
1/2 Rate
1/4 Rate
1/8 Rate
4 kbps
2 kbps
0.8 kbps
8.55 kbps
Encoder
Decoder64 kbps
PCM
20 ms Packets
Link Waveform
CDMA Forward Link WaveformPilot ChannelSync ChannelPaging ChannelTraffic Channel
CDMA REVERSE Link WaveformAccess ChannelTraffic Channel
QTSO
QTSO
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Rate ½, L = 9
Convolutionencoder
withrepetition
Data
9.6 kbps 4.8 kbps2.4 kbps1.2 kbps
Blockinter-leaver × × ×
× + ×Basebandshaping
filter
× + ×Basebandshaping
filter
-90 deg.
Carriergenerator
To
transmitter
PN codegeneratorQ channel
PN codegeneratorI channel
Long codegenerator Decimator
Hadamard(Walsh)sequence
Mask
Block diagram of IS-95 forward link
Pilot channeland othertrafficchannels insame cell
Pilot channeland othertrafficchannels insame cell
Reverse CDMA Channel
AccessCh 1
TrafficCh 1
TrafficCh m
• • • AccessCh n
REVERSE CDMA CHANNEL(1.23 MHz channel received by
base station)
• • • • • • • • • • • • • • • • • • • • • • • •
Addressed by Long Code PNs
Reverse Traffic Channel Structure for Rate Set 1
9.6 kbps 4.8 kbps 2.4 kbps 1.2 kbps
Convolutional Encoder
r=1/3, K=9
Reverse Traffic Channel
Information Bits
(172, 80, 40, or 16 bits/frame)
Code Symbol
Code Symbol
28.8 ksps
Add 8 bit Encoder Tail
Add Frame Quality Indica- tors (12, 8, 0,
or 0 bits/frame)8.6 kbps 4.0 kbps 2.0 kbps 0.8 kbps
1/2 PN chip Delay = 406.9 ns
D Q(t)
I(t)Baseband Filter
Baseband Filter
Data Burst Randomizer
I-channel Sequence 1.2288 Mcps
Q-channel Sequence 1.2288 Mcps
I
Q
Long Code
Generator
PN chip 1.2288 Mcps
Long Code Mask
Frame Data Rate
s(t)Σ
28.8 ksps 14.4 ksps 7.2 ksps 3.6 ksps
28.8 ksps
64-ary Orthogonal Modulator
Modulation Symbol
(Walsh chip)
4.8 ksps (307.2 kcps)
Block Interleaver
Symbol Repetition
Code Symbol
cos(2πfct)
sin(2πfct)
Summary of Parameters in IS-95 System
System Parameters Specification
Uplink frequency band 824-849 MHz
Downlink frequency band 869-894 MHz
Number of carriers/band 20
Multiple-access method CDMA
Number of users/carrier 60
Chip rate 1.2288 Mbps
Speech coder Variable rate, CELP
Speech rate 9600, 4800, 240, 1200
Interleaver Block
Channel encoder R=1/2,L=9(D), R=1/2, L=9(U)
Modulation BPSK with QPSK spreading (D)64-ary orthogonal with QPSK spreading (U)
Signature sequences Hadamard (Walsh) of length 64
PN sequence 242-1 (long code), 215 (spreading codes)