In this letter, we propose modifications to existing transmit-diversity techniques to provide transmit diversity in code-division multiple-access cellular systems which must support both second-generation and third-generation mobiles on a common carrier. The proposed method, which we call symmetric-sweep transmit diversity, combines phase-sweep transmit diversity (PSTD) and space-time spreading (STS) in a way that allows second-generation and non-STS-capable mobiles to obtain the full advantage of PSTD, while third-generation mobiles obtain the full advantage of STS.

Third-generation code-division multiple access (CDMA) cellular systems incorporate a downlink transmission technique called transmit diversity (TD). This paper provides a comprehensive investigation of the performance and practical implementation issues of open-loop transmit diversity schemes for the IS-2000 third-generation cellular CDMA standard. Discussed in detail are orthogonal transmit diversity (OTD) and space-time spreading (STS) diversity schemes. STS is a TD technique that is motivated by space-time coding principles originally described for narrowband systems. OTD is a TD technique that obtains diversity not at the symbol level, but in the decoding process, and has performance that is in general lower bounded by STS, which obtains diversity combining prior to decoding. Thus, STS always outperforms OTD, with the improvement particularly significant in the presence of weak convolutional codes. Probability of error analysis is performed for STS under the assumptions of imperfect channel estimates, correlation between antennas, and unequal pilot power allocations. Extensions to STS are provided for the multicarrier version of the standard and four transmit antennas. Simulation studies are performed to detail the performance of both open-loop TD schemes with convolutional coding and closed-loop power control consistent with the 3GPP2/IS-2000 standard. Many of these results were generated in the course of the IS-2000 standardization procedure. Performance is studied in radio environments which experience flat Rayleigh fading, frequency selective Rayleigh fading, spatially selective fading, as well as Ricean fading with various K factors. Some additional results are presented for cases where mobile receivers have two receive antennas. Implementation issues are also considered including the impact of antenna delay differences on performance, transmitter and receiver architectures, and computational complexity.

With the advent of new wireless mobile Internet technologies, there has been a significant increase in demand for capacity on the forward link of cellular systems. While significant enhancements to the system have improved the performance of the system, there continues to be a greater need for even more capacity on the forward link. Further capacity can only be derived by exploiting the spatial distribution of users. By intelligently steering energy related to a mobile only in the direction of a mobile, capacity can be increased. Use of intelligent antenna techniques coupled with transmit diversity techniques offer the most robust performance gains across a variety of environments. This paper discusses an antenna array architecture which exploits a combination of diversity and coherent antenna arrays to achieve peak performance in a cdma2000 environment. Performance results are given for this antenna architecture under a number of fading conditions.

Reliable performance is very important for high speed channel equalizers and echo cancellers used in high speed communications channels. A common type of hardware fault occurs when the coefficients get "stuck" at an uncontrollable value. Such faults lead to larger overall mean square errors, and generally poor performance. Redundancy can provide the ability to compensate for these types of faults if the proper design is introduced into the adaptive filter structure. Unfortunately this form of redundancy can lead to poor convergence performance for the adaptive filter after the fault occurrence. This paper examines the use of affine projection and row projection techniques to improve the convergence performance of the fault tolerant adaptive filtering structure. Algorithms are developed for two cases: fault knowledge and no fault knowledge incorporated in the adaptive filtering update. These algorithms are introduced in this paper and simulations are presented to illustrate the effectiveness of these approaches.