ikom - ComNets

April 23, 2010 1

Wireless Network Virtualization LTE case study

Yasir ZakiComNets – TZI

University of Bremen, GermanyApril 23rd, 2010

ikom - ComNets

April 23, 2010 2

Outline

Introduction to Wireless Virtualization

State-of-the-art

LTE Virtualization Motivation, Issues and Proposal

Simulation Model and Results

Conclusion and Outlook

ikom - ComNets

April 23, 2010 3

Introduction to Wireless Virtualization

A nature extension from wired to wireless virtualization

Virtualization techniques of the wireless medium look for the use of the physical network in a slotted way

Virtualization of the wireless resources on the air interface is a scheduling problem of:

– Tx/Rx power– Frequency– Time– Code – Space allocation

Issue: the wireless links suffer more interference than the wired ones

Time

Time

ikom - ComNets

April 23, 2010 4

Virtual Radio*

* J. Sachs, S. Baucke, “Virtual Radio-A Framework for Configurable Radio Networks”; WICON’08, Hawaii, USA, Nov. 2008.

Defines a framework for configurable radio networks

It extends the network virtualization concept into the wireless domain known as “radio virtualization”

– Different virtual radio networks can operate on top of a common shared infrastructure and share the same radio resources

It presents how the radio resource sharing can be performed efficiently without interference between the different virtual radio networks

ikom - ComNets

April 23, 2010 5

VANU MultiRAN*Vanu- MultiRAN™ Virtual Base Station is a commercial software

Taking advantage of Vanu software RAN technology, MultiRAN was developed to support multiple virtual base stations (vBTS) running on a single BTS hardware platform. The expense of antennas, BTS electronics, and backhaul can all be shared.

* J. Chapin; “Overview of Vanu Software Radio”; from http://www.vanu.com, June. 2009.

ikom - ComNets

April 23, 2010 6

Our LTE Virtualization Proposal

© 4WARD Consortium

ikom - ComNets

April 23, 2010 7

LTE Virtualization - Motivation

For the infrastructure providers:– Saving OPEX and CAPEX

For the virtual mobile system operators:– Lower barrier for the smaller players going to the market– Flexibility for network coverage– Re-configurability

For the end-user:– Diversity of services– Lower price per bit (?)

Others:– Power saving in rural areas– ......

ikom - ComNets

April 23, 2010 8

LTE Virtualization - Issues

Radio Resource Management (RRM) and Scheduling

Inter-operator interference modeling and management

Radio Network Planning and Optimization

System level evaluation

......

ikom - ComNets

April 23, 2010 9

LTE Hypervisor

The LTE hypervisor is responsible for virtualizing the eNB and scheduling the air interface (OFDMA) resources among the Virtual Operators (VOs)

The hypervisor collects all relevant information (from all VOs) regarding their users channel conditions, traffic load, VO requirements, VO contracts, etc.

Based on these information, the hypervisor tries to allocate the resources to the VO according to what best fits the different requirements

ikom - ComNets

April 23, 2010 10

LTE Hypervisor cont.In LTE each operator has his own bandwidth to use

This Bandwidth will translate into a number of available Physical Resource Blocks (PRBs)

– This is the smallest unit to be scheduled for a user– One PRB consists of 12 subcarriers ~ 180 kHz

The Hypervisor is responsible for allocating the PRBs into the virtual operators eNBs

The individual virtual eNB MAC scheduler will then schedule these PRBs into his own UEs

The Hypervisor can make use of the current information to schedule the PRBs:

1. Channel Quality Indicators of UEs (CQI)2. Buffer Occupancy of UEs3. Predefined Contracts of the VOPs (bandwidth reservation)4. Available number of UEs in each VOPs5. etc.

Physical Resources

PRBs

Hypervisor (2nd level Scheduler)

Physical eNB

Virtual eNBs

LTE MAC Scheduler

LTE MAC Scheduler

LTE MAC Scheduler

Channel Conditions

ikom - ComNets

April 23, 2010 11

VNet Operator Contracts

The VNet operator will lease resources from the infrastructure provider, this could be done based on predefined contracts

– The contract specifies the requested resources, i.e. memory, CPU, storage, etc.– In addition it specifies the required spectrum to be used by the operator

We define mainly four different contract types:– Fixed guarantees: the operator requests a fixed bandwidth that would be allocated to it all the time

whether it will be used or not

– Dynamic guarantees: the operator requests a guaranteed maximum bandwidth that would be allocated to the operator if required, otherwise only the actual need would be allocated

• The operator might only pay based on the used bandwidth which could save cost

– Best effort with minimum guarantees: the operator specifies a minimum guaranteed bandwidth which will be allocated at all time; and a maximum value that would act as an upper bound. The allocation will be done in a BE manner

– Best effort with no guarantees: the operator would only be allocated part of the bandwidth if the current load permits i.e. in a pure BE manner

ikom - ComNets

April 23, 2010 12

Hypervisor Scheduler

In order for the hypervisor to be able to satisfy the operator requests and their predefined contracts, an estimate of the actual needed spectrum of each operator is required

The operators need to feedback this estimate value back to the hypervisor (in a predefined time interval)

The PRBs estimate of each operator can be calculated iteratively as follows:

Est(n) is the average PRBs estimate count after n number of TTIs*PRBs_TTI(n) is the instantaneous PRBs count needed by the operator by the nth TTIn is the number of TTIs in the hypervisor allocation time interval (granularity)

*TTI: transmission time interval (in LTE it is 1 ms)

ikom - ComNets

April 23, 2010 13

Hypervisor SchedulerThe hypervisor allocates the PRBs on the different virtual operators as follows:

1. Firstly, allocate PRBs to operators with the “fixed guaranteed” contract

2. Secondly, allocate PRBs to operators with the “dynamic guaranteed” contract based on the estimate number of PRBs (Est(n)), this should be upper bounded by the max value defined in their contract

3. Then, allocate PRBs to operators with the “BE with minimum guarantees” contract based only on the minimum value defined in their contract, this is to guarantee the minimum value

4. Finally, whatever left number of PRBs would be allocated to the BE operators with “BE with minimum guarantees” and “BE with no guarantees” contracts

The allocation of the left PRBs to the BE operators in step 4 will be done based on a Fair Factor (FF) which is defined as follows:

ikom - ComNets

April 23, 2010 14

Simulation Model and Results

© 4WARD Consortium

ikom - ComNets

April 23, 2010 15

Hypervisor

OPNET Simulation Model

Physical eNB

Virtual eNBs

ikom - ComNets

April 23, 2010 16

Simulation Configuration

The traffic modes used are configured as follows:

The simulation is configured with 4 virtual operators each with one of the different contract types defined earlier:

1. Video streaming operator: with a fixed guaranteed contract of 33 PRBs

2. VOIP operator: configured with a dynamic guaranteed contract, with a max value of 33 PRBs

3. VOIP + BE Video on demand operator: configured with the best effort with min. guarantees contract, with min. and max. value of 25 and 45 consecutively

4. Small VOIP operator: configured with BE and no guarantees contract

Two scenarios are configured one without virtualization “legacy” and one with virtualization “virtualized”.

Table 2

ikom - ComNets

April 23, 2010 17

Virtual Operator (VO) allocated number of PRBs

The figure shows the number of PRBs that each virtual operator has been allocated over time

It can be noticed that for the first operator the PRBs allocation is fixed to 33 PRBs

– since it is using the fixed guaranteed contract

For the other three operators we can notice that the allocated number of PRBs changes with time depending on the traffic load and the contract details of each operator

ikom - ComNets

April 23, 2010 18

Virtual operator 1 (12 video users)Air interface throughput and app. end-to-end delay

What can be noticed is that the operator has the same performance with and without virtualization; this is because this operator has a contract with a guaranteed fixed allocation

ikom - ComNets

April 23, 2010 19

Virtual operator 2 (40 VOIP users)Air interface throughput

What can be noticed is that the operator has the same performance with and without virtualization

ikom - ComNets

April 23, 2010 20

Virtual operator 2 (40 VOIP users) Application end-to-end delay

The application end-to-end delay of the operator has the same performance with and without virtualization

ikom - ComNets

April 23, 2010 21

Virtual operator 2Downlink used number of PRBs vs. time

The previous results showed that operator 2 has the same performance with and without virtualization

But, in the “virtualized” scenario operator 2 is not wasting the air interface resources since it only uses the required number of PRBs to serve the users as can be seen in the figure

This is a big advantage since the operator will be able to cut cost because he will only pay for the resources used

ikom - ComNets

April 23, 2010 22

Virtual operator 3 (16 VOIP+16 video users)Air interface throughput

It can be noticed that users 1 – 16 (which are the VOIP users) have the same performance in both scenarios, whereas users 17 – 32 (Video users) are having a slightly better performance in the “virtualized” scenario.

ikom - ComNets

April 23, 2010 23

Virtual operator 3 Application end-to-end delay

For the VOIP users (left side figure) we can see that similar performance is achieved in both scenarios. As for the video users (right side figure) one can notice that users are suffering from huge delay values for the “legacy” scenario due to buffering; whereas in the “virtualized”scenario the users are having good performance.

The reason why the VOIP users in the “legacy” scenario are not affected is the fact that these users are being served with higher priority and the resources are enough to serve those users, but not enough to serve the video users.

ikom - ComNets

April 23, 2010 24

Virtual operator 4 (3 VOIP users)Air interface throughput and app. end-to-end delay

One additional advantage that can be achieved in the “virtualized” scenario is the ability to serve small operators with relatively smaller number of users in a pure best effort manner with whatever resources are left rather than wasting these resources

ikom - ComNets

April 23, 2010 25

ConclusionThe results demonstrate the additional advantages that can be achieved from applying network virtualization into the wireless world (in addition to being able to share the infrastructure and being able to change resources dynamically)

Both operator 2 and 3 benefited from virtualization where:– Operator 2 is able to cut costs by being able to use and pay only with respect to what he needs

while still being able to guarantee his users performance– Operator 3 is able to serve his users with better performance gaining from the use of the left

resources

The results also show the possibility of opening the market to new players (mainly small operators) that can serve very specific rule and have in general small number of users

– These operators can operate with the left number of resources that are normally not used and wasted in today’s network

ikom - ComNets

April 23, 2010 26

OutlookThis work is a starting point of the LTE virtualization, as there are more issues to be investigated:

– Interference coordination among multiple virtual operators– Signaling overhead due to the hypervisor in charge of the resource allocation– Defining guidelines and scheduling disciplines for the hypervisor based on

more enhanced criteria/contracts– More diverse simulation scenarios – …..

Nevertheless, with LTE wireless virtualization operators can expect not only lower investment for flexible network deployment but also lower costs for network management and maintenance, meanwhile the end-user can expect better services with lower prices in the future.

ikom - ComNets

April 23, 2010 27

Questions

ikom - ComNets

April 23, 2010 28

BACKUP

ikom - ComNets

April 23, 2010 29

LTE Downlink Physical Resources Structure

Inter-carrier subspacing15 kHZ Sub-carrier

Frequency (Hz)

Time (

sec)

Resource

elemen

t

QPSK 2bits

16QAM 4b

its

64QAM 6b

its

7 OFDM sy

mbols

0.5 m

s

12 Subcarriers12*15k=180kHz

1 Phys

ical

resource

block

(PRB)