Abstract
We study the performance of joint signature-receiver optimization for direct-sequence code-division multiple access (DS-CDMA) with limited feedback. The receiver for a particular user selects the signature from a signature codebook, and relays the corresponding B index bits to the transmitter over a noiseless channel. We study the performance of a random vector quantization (RVQ) scheme in which the codebook entries are independent and isotropicany distributed. Assuming the interfering signatures are independent, and have independent and identically distributed (i.i.d.) elements, we evaluate the received signal-to-interference plus noise ratio (SINR) in the large system limit as the number of users, processing gain, and feedback bits B all tend to infinity with fixed ratios. This SINR is evaluated for both the matched filter and linear minimum mean-squared error (MMSE) receivers. Furthermore, we show that this large system SINR is the maximum that can be achieved over any sequence of codebooks. Numerical results show that with the MMSE receiver, one feedback bit per signature coefficient achieves close to single-user performance. We also consider a less complex and suboptimal reduced-rank signature optimization scheme in which the user's signature is constrained to lie in a lower dimensional subspace. The optimal subspace coefficients are scalar-quantized and relayed to the transmitter. The large system performance of the quantized reduced-rank scheme can be approximated, and numerical results show that it performs in the vicinity of the RVQ bound. Finally, we extend our analysis to the scenario in which a subset of user optimize their signatures in the presence of random interference.
Original language | English (US) |
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Pages (from-to) | 3475-3492 |
Number of pages | 18 |
Journal | IEEE Transactions on Information Theory |
Volume | 51 |
Issue number | 10 |
DOIs | |
State | Published - Oct 2005 |
Funding
Manuscript received October 18, 2004; revised June 20, 2005. This work was supported by the U.S. Army Research Office under Grant DAAD19-99-1-0288 and the National Science Foundation under Grant CCR-0310809. The material in this paper was presented in part at IEEE International Symposium on Spread Spectrum Techniques and Applications (ISSSTA 2002), Prague, Czech Republic, September 2002 and the IEEE International Symposium on Information Theory, Yokohama, Japan, June/July 2003.
Keywords
- Asymptotics
- Code-division multiple access (CDMA)
- Feedback
- Large system analysis
- Reduced-rank signature
- Signature optimization
- Vector quantization
ASJC Scopus subject areas
- Information Systems
- Computer Science Applications
- Library and Information Sciences