Power Control and Rate Adaptation in WCDMABy Olufunmilola Awoniyi

ContentsOverview of WCDMAPaper summary - GoalSystem Model and Assumptions Approach Simulation Results Comments

WCDMAThird generation wireless systems designed to fulfill the communication to anybody, anywhere, anytime vision.Support voice, streaming video, high speed data. Spread spectrum systems with spread bandwidth of >=5MHzSupport multirate services by using spreading codesDifferent versions of WCDMA check for names of standards - Europe - UMTS (asynch). - Japan - Core-A (asynch) - Korea - TTA (I & II) (TTA I synch, TTA II asynch) - US - CDMA2000 (synch) - ITU - IMT-2000

*ARIB Association of Radio Industries and Businesses *ETSI European Telecommunications Standardization Institute *IMT- 2000 International Mobile Telecommunications 2000 *ITU - International Telecommunication union *TIA Telecommunication Industry Association*TTA Telecommunication Technology Association *UMTS - Universal Mobile Telecommunications System

WCDMA StandardsIMT-2000 proposal

Features of the WCDMA

Bandwidth5, 10, 20 MHz Spreading codesOrthogonal variable spreading factor (OVSF) SF: 4-256Scrambling codesDL- Gold sequences. (len-18)UL- Gold/Kasami sequences (len-41)Data ModulationDL - QPSKUL - BPSKData rates144 kbps, 384 kbps, 2 MbpsDuplexing FDD

UL and DL SpreadingUplink Transmitter Design

Paper SummaryPower and rate allocation in multirate wideband CDMA system by J.W Mark and S. Zhut ( University of Waterloo)

Goal Develop a power distribution law the IMT-2000 WCDMA system so that the QOS requirements are met and transmit power is minimized.

Conclusion - Power adaptation is a function of spread bandwidth, data rates and QOS requirements. - The closer the demand for resource is to the available resource, the higher the required transmit power.

System ModelUplink transmissions in a single cell bottle-neck for capacity M users in the cellNumber of channels for user j is Kj where Kj L Channel AWGN, denoted by nj for the jth userTotal Interference (Itj) = Thermal noise + MAI Gaussian QOS elements have factored in fading and shadowing effects specified in terms of SIR (BER), j,, such that with data rates Rbj, where

Total transmit power required (to transmit over Kj channels) for user j is Sj Each user have a traffic demand, j, and a normalized traffic demand, j.

* MAI Multiple access interference

System Model - Equations can be written in SIR terms as,

such that the required transmit power is

Therefore, Sj can be define as

with a normalized traffic demand defined as Total interference is

* W Spread bandwidth

Approach (1) If S = [S1, S2,,SM ], with some manipulation, such thatPerron-Frobenius Theorem p has positive eigenvalue, equal to the spectral radius and if < 1, the solution is non- negative. Example - M = 2 - By solving the characteristic polynomial, det[p- IM] = 0 - 1= 2 = , n1 = n2 = n (uniform traffic demands and noise)

Observations - - For any power distribution, traffic demand is upper bounded by spread bandwidth. - The higher the noise or the closer the traffic demands are to W, the higher the required transmit power.

Approach (2)Limiting case Ignore n for each user and minimize transmit power - By solving for a non-trivial solution, for uniform traffic demands, therefore, (necessary condition for convergence - 1) and

Observation - All users transmit the same power and raise the transmit power until interference can be ignored

Approach (3)General case - If Sj is such that Therefore,

Consequently,

(necessary condition for convergence - 2)

Admission policy The conditions sufficient for convergence will used to accept or reject a request for connection in the admission controller. 1) For all s (for users already connected and those requesting), calculate E() and Var() such that

2) Admission policy - Admit -

- Reject -

- Admit light traffic demand - and

Simulation Results The higher the variation in the normalized traffic demand, the looser the bound and the higher the capacity. Uniform traffic achieves the minimum capacity.At M , the variation in traffic becomes less significant and the distribution of the traffic demand looks uniform. Admission of a new call can lead to other users having to change their transmit power to achieve their desired SIR values.

CommentsWorst case scenario - When most users increase their transmit power to meet QOS constraints, the system blows up. - Total traffic demand < 0.8W. - Better to have power constraints (average or total power).

Multicell system - Link Quality in SIR Based Power Control for UMTS CDMA system by Oppermann et al. Fading / ISI channel - Adaptive Multicode CDMA for the uplink Throughput Maximization by S.A Jafar and A. Goldsmith