Packet Success Probability Research Articles

Multiple-capture performance of DS-SS packet radio systems with common spreading code

The author presents a multiple-capture model for the centralised spread-spectrum (SS) packet radio systems in which each user is assigned common direct-sequence (DS) spreading code for packet transmission. Basic equations for the multiple-capture probability and throughput performance are derived at the central receiver. At the link-level, two key design parameters in common spreading code systems are evaluated, namely, the expected number of packets captured at the receiver and the allowable number of simultaneous transmissions that are supportable at a specified data bit-error rate and probability of packet capture. Using the block oriented systems simulator (BOSS), simulations were carried out for the central receivers with coherent, differential, and envelope header detection, and results from the simulations are compared with theoretical evaluations of the multiple-capture probability. It is shown, for a threshold approximation to the probability of data packet success, that the multiple-capture model significantly improves system throughput.

Performance improvement of a frequency hopping-CDMA system utilizing memorized prior data

An algorithm for improving the stability and throughput of a frequency hopping code-division multiple-access system (FH-CDMA) is presented. The algorithm includes a multiple block transmission with error-detection block(s) and a logical AND-operation between previously received (erroneous but saved) data, and retransmitted data. The packet success probability of the new algorithm is formulated and the improvement in stability is shown in terms of the proportion of retransmission users in the system under various conditions, including the new packet generation probability, retransmission probability, different signal-to-noise ratio in the channel, and the number of blocks in a packet. The average drift of retransmission users and the analysis of the expected number of retransmissions were used to evaluate the stability performance of the retransmission strategy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance Evaluation of Unslotted Random Access Packet CDMA Channels

This paper presents an analytical performance evaluation model for a class of unslotted random access packet CDMA (code division multiple access) channels. In the system considered, many interactive terminals asynchronously transmit (uncoded) spread spectrum modulated variable length data packets on a shared wideband channel. Since unslotted operation at the physical level precludes the application of controlled multiaccess procedures, reliable link level operation is achieved using an ALOHA-Iike procedure in which incorrectly received packets are retransmitted with random delay. In view of the resulting traffic dependent packet success probability, Rich a packet CDMA (or “spread ALOHA”) channel may be expected to exhibit throughput and stability properties qualitatively similar to those of narrowband ALOHA. A flow equilibrium based analytical model for performance evaluation is presented and used to illustrate both throughput-delay and stability characteristics for an example random code direct sequence (DS) unslotted CDMA system. It is shown that a typical uncoded packet DS-CDMA channel achieves a maximum bandwidth normalized throughput (utilization) in the region of 0.15–0.2, and is thus competitive with narrowband ALOHA carrying similar data traffic. Stability issues for finite-population channels are also addressed, leading to the conclusion that relatively long average retransmission delays may often be required to prevent bistable behaviour unless adaptive policies are nsed.

Bit-to-bit error dependence in slotted DS/SSMA packet systems with random signature sequences

A technique is developed to find an accurate approximation to the probability of data bit error and the probability of packet success in a direct-sequence spread-spectrum multiple-access (DS/SSMA) packet radio system with random signature sequences. An improved Gaussian approximation to the probability of data bit error is performed. Packet performance is analyzed by using the theory of moment spaces to gain insight into the effect of bit-to-bit error dependence caused by interfering signal relative delays and phases which are assumed constant over the duration of a desired packet. Numerical results show that if no error control exists in the desired packet or if block error control is used when multiple-access interference is high, the error dependence increases the average probability of packet success beyond that predicted by models which use independent bit errors. However, when block error control is used and the multiple-access interference is low, the bit error dependencies cause a reduction in packet error performance. >