Li Fung Chang

Signal and interference statistics of a CDMA system with feedback power control

A feedback power control approach that allows power commands to be updated at a higher rate than the rate of multipath fading is investigated. The signal and interference statistics as received at the base stations after power control are obtained for a simulated direct-sequence code-division multiple-access (CDMA) system, which includes multiple base stations with diversity receivers and a large number of power-controlled users continuously moving at various speeds. It is shown that often-used analyses based on perfect average power control lead to optimistic capacity results (by 25% to 60%) because interference is underestimated by 1 to 2 dB.<<ETX>>

Performance of a CDMA radio communications system with feed-back power control and multipath dispersion

An investigation is made of the performance of a CDMA (code-division multiple access) radio system with feedback power control. Feedback power control delay, power delay profile and channel fading rate are used as parameters to characterize the channel performance. Tradeoffs between the use of single and multiple correlators per antenna for the multipath dispersive channel are shown. It is found that in some delay-spread environments, it may be better to turn off one of the correlators or lock all the correlators onto the strongest path.<<ETX>>

Architecture and implementation of an efficient and robust TDMA frame structure for digital portable communications

The architecture and implementation of a TDMA (time-division multiple access) digital portable communication system using short bursts are considered. The authors describe an efficient and robust TDMA frame structure that requires very low overhead for burst demodulation and synchronization while being robust against both fading and carrier frequency offset. Based on this frame structure, an experimental radio link was implemented, using a hardware architecture that is suitable for digital signal processing and VLSI implementation. Performance results are presented.<<ETX>>

Comparison of two convolutional orthogonal coding techniques for CDMA radio communications systems

For CDMA (code-division multiple-access) wireless communications systems, orthogonal signaling with noncoherent detection has been proposed when a reference phase is not available. In this paper, orthogonal signaling using Walsh signals is considered. Performance of the channel using error-correcting coding together with 1) bit-by-bit interleaving or 2) Walsh word-by-word interleaving is investigated. Simulation results show that for several types of fading and non-fading channels with practical amounts of interleaving and with practical power control, the second technique with complete soft decision decoding that has added complexity in the decoder gives significant reduction in the required signal to interference ratio (SIR) over the first technique. >

Outage probability for a frequency-selective fading digital portable radio channel with selection diversity using coding

The outage probability for a time division multiple access (TDMA) portable radio channel with diversity selection based on coding is obtained by using computer simulation. Coherent detection of a quaternary phase shift keying (QPSK) signal with spectrally raised-cosine Nyquist pulse with 0.5 roll-off factor is used as an example. Different performance criteria are used to define outage. The outage probability as a function of the normalized RMS time delay spread is then used to determine the maximum transmission rate than can be supported by a portable radio channel. It is found that for a performance objective of 1% or less outage, a transmission rate of several hundred kb/s is possible. The use of two-branch selection diversity can increase the channel capacity by about a factor of 3 or more.<<ETX>>