Roy Thomas Derryberry

Transmit diversity in 3G CDMA systems

Transmit diversity (TD) is one of the key contributing technologies to defining the ITU endorsed 3G systems W-CDMA and cdma2000. Spatial diversity is introduced into the signal by transmitting through multiple antennas. The antennas are spaced far enough apart that the signals emanating from them can be assumed to undergo independent fading. In addition to diversity gain, antenna gain can also be incorporated through channel state feedback. This leads to the categorization of TD methods into open loop and closed loop methods. Several methods of transmit diversity in the forward link have been either under consideration or adopted for the various 3G standards. This article describes the concept of transmit diversity and explains the features of selected TD techniques.

Performance of closed loop transmit diversity with feedback delay

Closed loop multi-antenna diversity transmission methods are being considered for 3/sup rd/ generation wireless standards. In these techniques, information about the downlink channel is fed back to the base station and utilized to provide diversity as well as antenna gain at low mobile velocities under flat fading conditions. The performance, however, drops at higher velocities, mainly due to the delay involved in the feedback of antenna weights. We analyze this behavior, with the aim of quantifying the degradation in average received signal power as a function of velocity. The two cases of complex weight feedback and pure phase feedback are considered. The analysis will help to determine a useful velocity range in which closed loop diversity is feasible.

Transmit adaptive array without user-specific pilot for 3G CDMA

The transmit adaptive array (TxAA) is one of the promising closed-loop downlink diversity schemes being considered for the third generation wireless systems based on code division multiple access (CDMA). The TxAA technique originally proposed, requires a user-specific auxiliary pilot for coherent demodulation. This affects the capacity of the system due to additional power being used by this pilot. The mobile receiver requires additional hardware correlators for demodulating the pilot. Since different channels in spread spectrum systems are distinguished by their spreading sequences, it also uses up an additional Walsh code per user. This paper proposes a decision directed method for demodulation which does not require a user-specific pilot. Our simulations demonstrate that the performance of the technique is comparable to that of the method based on a user specific pilot.

Reverse high-speed packet data physical layer enhancements in cdma2000 1/spl times/EV-DV

The rapid growth of Internet-based applications calls for design of a high-speed wireless packet data communication system. This anticipated increase in future mobile wireless packet data services has challenged the current 3G standardization bodies to respond with evolved 3G system specifications capable of providing increased data throughput. In response to such a need, 3GPP2 recently completed the enhanced reverse link standardization effort of the CDMA technology flagship, cdma2000/spl reg/ by completing the definition of the 1/spl times/EV-DV 1/spl times/ system. 1/spl times/EV-DV achieves higher data throughput while simultaneously providing coexisting and backward-compatible voice services within the same spectrum. This feature of 1/spl times/EV-DV allows wireless operators to manage the voice and data loading in their system more efficiently. This article describes the physical layer reverse link enhancements in cdma2000 revision D that are necessary to support 1/spl times/EV-DV.