Frequency-hop Spread-spectrum Packet Research Articles

Hermitian codes for frequency-hop spread-spectrum packet radio networks

Hermitian codes are an attractive alternative to Reed-Solomon codes for use in frequency-hop spread-spectrum packet radio networks. For a given alphabet size, a Hermitian code has a much longer block length than a Reed-Solomon code. This and other considerations suggest that Hermitian codes may be superior for certain applications. Analytical results are developed for the evaluation of the packet error probability for frequency-hop transmissions using Hermitian coding. We find there are several situations for which Hermitian codes provide much lower packet error probabilities than can be obtained with Reed-Solomon codes. In general, as the code rate decreases or the symbol alphabet size increases, the relative performance of Hermitian codes improves with respect to Reed-Solomon codes. Performance evaluations are presented for an additive white Gaussian noise channel and for certain partial-band interference channels, and the packet error probability is evaluated for both errors-only and errors-and-erasures decoding.

PERFORMANCE ANALYSIS OF FREQUENCY-HOPPED SPREAD-SPECTRUM PACKET RADIO NETWORKS PART II: UNSLOTTED MULTIPLE-ACCESS

This paper is concerned with the performance analysis of unslotted frequency-hopped spread spectrum packet radio networks with Reed-Solomon forward error control coding. The following different network alternatives are analyzed in a unified manner (i) random/one-coincidence frequency hopping patterns, (ii) one/several code symbols per dwell interval, (iii) independent/dependent packet arrival processes, (iv) fixed/variable length packets. Joint probability generating functions for the pair-wise hit patterns and the effective multiple-access interference vector are determined for the different alternatives. Closed form formulae and expressions for packet capture probabilities are readily obtained from these generating functions. A direct proof is given that in the case of single symbol/dwell packets symbol errors, are asymptotically independent. Numerical results indicate that the unslotted networks outperform the corresponding slotted ones at low to moderate traffic levels, and the difference between the two networks is diminishing when the number of frequency bins is large.

A slotted frequency-hopped multiple-access network with packet combining

A frequency-hopped spread-spectrum (FH/SS) packet radio network is considered. Instead of discarding the received packets which were unsuccessfully decoded, the receiver keeps and combines the different received copies of the same packet to improve the throughput and reduce the delay necessary to transmit a packet successfully. It is shown that the throughput is substantially increased over a similar system where the uncorrectable packets are discarded. This system is equivalent to a fast frequency-hopped system where the diversity level is adapted according to the channel conditions. Reed-Solomon (RS) codes are used for error correction and detection.

Adaptive forwarding in frequency-hop spread-spectrum packet radio networks with partial-band jamming

Adaptive protocols that specify the ways in which a radio is permitted to modify its normal forwarding procedures based on information obtained locally in the network are considered. A computer program has been developed to simulate a frequency-hop (FH) packet radio network with partial-band jamming and interference due to other FH and narrowband radios. The radios in the network use time-slotted, receiver-directed, FH spread-spectrum signaling. Results on throughput, delay, and end-to-end probability of success are presented, and comparisons between different forwarding protocols are given for a static network topology with both static and mobile network jamming. >

Correction to 'Packet error probabilities in frequency hopped spread-spectrum packet radio networks-memoryless frequency hopping patterns considered'

The author corrects the approach followed in the above-titled paper (see ibid., vol.36, no.6, p.720-3, 1988) to compute packet error probabilities in frequency-hopped spread-spectrum packet radio networks with memoryless frequency-hopping patterns. The nature of the error is that the sequence of symbol errors is not Markov, so that a formula which is instrumental for the computation of packet error probabilities, is incorrect. He obtains exact and easy to compute expressions for the evaluation of the packet error probabilities.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comments on "Packet error probabilities in frequency-hopped spread-spectrum packet radio networks-memoryless frequency-hopping patterns considered

In the above-titled paper by M. Georgiopoulos (see ibid., vol.36, no.6, p.720-3, 1988), the packet error probability induced in a frequency-hopped spread-spectrum packet radio network is computed by using the Markovian property of the byte errors at the receiver. It is shown here that the byte errors at the receiver do not exhibit a Markovian structure. A correct analysis and numerical results are provided.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comments on "Packet error probabilities in frequency-hopped spread-spectrum packet radio networks-memoryless frequency-hopping patterns considered" by M. Georgiopoulos

The authors demonstrate that contrary to the claim made in the above named work (ibid., vol.36, Jun., p.720-3, 1988), the sequence of hits in an asynchronous frequency hop multiple-access system is not a Markov process. Comments of the use of a model in which the hits are independent are also given. >

Packet error probabilities in frequency-hopped spread-spectrum packet radio networks-memoryless frequency-hopping patterns considered

The packet error probability induced in a frequency-hopped spread-spectrum packet radio network is computed. The frequency spectrum is divided into q frequency bins. Each packet is exactly one codeword from an (M, L) Reed-Solomon code (M=number of codeword symbols (bytes); L=number of information symbols (bytes)). Every user in the network sends each of the M bytes of his packet at a frequency chosen among the q frequencies with equal probability and independently of the frequencies chosen for other bytes (i.e., memoryless frequency-hopping patterns). Statistically independent frequency-hopping patterns correspond to different users in the network. Provided that K users have simultaneously transmitted their packets on the channel and a receiver has locked on to one of these K packets, the probability that this packet is not decoded correctly is evaluated. It is also shown that although memoryless frequency-hopping patterns are utilized, the byte errors at the receiver are not statistically independent; instead they exhibit a Markovian structure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>