Joint delay-power capture in spread-spectrum packet radio networks

Capture phenomena in slotted ALOHA packet radio networks employing spread-spectrum modulation is considered. Probability of capture with both delay and power capture mechanisms are derived and compared with power- and delay-only capture models. Significant improvements in the capture probability is observed. The improvement over the delay-only capture model increases with decreasing arrival-time randomization overhead     

Joint Delay-Power Multiple Packet Capture Scheme for Spread-Spectrum Slotted ALOHA Packet Radio Networks

In this paper, a joint delay-power multiple packet capture scheme, that can collect multiple packets simultaneously from different terminals with both delay and power captures, is presented. The corresponding joint delay-power capture probabilities for a spread-spectrum slotted ALOHA packet radio networks where all terminals use a common spreading code under Rayleigh fading with power control are derived. Throughput and delay performance of the spread-spectrum slotted ALOHA packet radio networks with the joint delay-power multiple packet capture effect are shown by our simulation results to be significantly improved compared with the existing schemes.     

Multiple-packet forwarding protocols for frequency-hop packet radio networks

Reliable data distribution within multiple-hop spread-spectrum packet radio networks requires high performance from the network protocols. The high variability in quality among the links and the unique characteristics of frequency-hop spread-spectrum signaling impose special requirements for network protocols that are to be employed in frequency-hop packet radio networks. These features can be exploited in the forwarding protocols by allowing multiple packets to be included in each forwarding attempt. The use of multiple-packet transmissions exploits the capture property of frequency-hop signaling, and it reduces the overhead required for acknowledgments. A potential trade-off arises because the use of multiple-packet transmissions increases the throughput, but in some situations it can also increase the delay. Two new transmission protocols that employ multiple-packet transmissions are described, and their performance is evaluated.     

Network protocols for frequency-hop packet radios with decoder sideinformation

Reliable data distribution within spread-spectrum packet radio networks requires high performance from the network protocols. This paper describes research in forwarding and routing protocols that are designed specifically for slow-frequency hop (SFH) packet radio networks in which some of the radios are subjected to excessive interference. It is shown that information extracted from the decoder can be used to aid the network protocols. New metrics are introduced that use this information to give a quantitative assessment of the interference environment experienced by the receiver in an SFH radio. Forwarding protocols are developed that can react quickly to local sources of interference, and the metrics that are introduced permit the routing algorithm to react to changes in the interference conditions in the network     

Performance analysis of spread spectrum packet radio network withchannel load sensing

A continuous-time Markov-chain model for an asynchronous communication spread-spectrum code-division-multiple-access (CDMA) packet radio network is developed. The network is composed of mutually independent users. The receiver-based code is considered; a terminal with a packet to send looks up the destination's code and transmits on that code. Each user senses the channel load and refrains from transmission if the channel load exceeds the channel threshold. The model makes it possible to study the threshold effect of channel load on the performance of the CDMA packet radio network. Improvements in performance of spread-spectrum packet radio networks due to channel-load sensing are shown. Steady-state results for throughput are obtained     

Threshold decision for PN code acquisition in direct-sequencespread-spectrum packet radio systems

A threshold decision for code acquisition in direct-sequence spread-spectrum packet radio systems is described. It is shown that this scheme achieves lower false alarm probability than the acquisition scheme based on the Neyman-Pearson criterion, giving comparable performance for the detection probability     

Performance analysis of frequency-hop packet radio networks with generalized retransmission backoff

A fully connected radio network is considered in which packets are sent using Reed-Solomon error-control coding, slow frequency-hop (FH) modulation, and generalized retransmission backoff policy. An easy-to-use analytical method for finite population FH networks is developed which offers insight into how system dynamics is affected by the number of users and the input rate. The performance of several retransmission backoff policies is examined. It is shown that the performance of exponential backoff policy with small minimum retransmission probability is not too far away from the optimum, when the code-block length is small and the number of users is not unreasonably large. It is also shown that packet rejection after a certain number of unsuccessful transmissions can stabilize some networks as one would expect, but may destabilize some others contrarily. Finally, the accuracy of the method is verified by extensive simulation results.     

A general approach to the evaluation and characterization of packet radio networks performance

In this work a general exact methodology for capture effect and performance evaluation of packet radio networks is presented. Both narrow-band and spread-spectrum systems are investigated and compared. Several network performance quality indexes are considered: throughput, outage probability, packet error probability, average delay time. Two particular capture effect models are investigated. It can be seen that one of the two models can be considered as a good approximation of the other if a appropriate parameter definition is made. By using this methodology various operating conditions given by fading (Rice, Rayleigh, Nakagami), shadowing, different traffic models, different modulation, and coding schemes are investigated. Comparison is performed by means of spectral efficiency parity.     

Unslotted CDMA with fixed packet lengths

The performance analysis of unslotted spread-spectrum packet radio network is very difficult because the received signal-to-noise ratio (SNR) fluctuates during the packet transmission. Past analyses are either based on complete enumeration or restricted to performance bounds. Here, a technique based on ballot theory is developed to analyze the performance of unslotted ALOHA spread-spectrum packet radio networks. This technique is also used to analyze the channel load sensing access protocol. An L-channel model is assumed     

A reservation random-access protocol for voice/data integratedspread-spectrum multiple-access systems

Most code-division multiple-access (CDMA) systems described in the literature provide only one single service (voice or data) and employ the strategy of “one-code-for-one-terminal” for code-assignment. This assignment, though simple, fails to efficiently exploit the limited code resource encountered in practical situations. We present a new protocol called reservation-code multiple-access (RCMA), which allows all terminals to share a group of spreading codes on a contention basis and facilitates introducing voice/data integrated services into spread-spectrum systems. The RCMA protocol can be applied to short-range radio networks, and microcell mobile communications, and can be easily extended to wide area networks if the code-reuse technique is employed. In RCMA, a voice terminal can reserve a spreading code to transmit a multipacket talkspurt while a data terminal has to contend for a code for each packet transmission. The voice terminal will drop a long delayed packet while the data terminal just keeps it in the buffer. Therefore, two performance measures used to assess the proposed protocol are the voice packet dropping probability and the data packet average delay. Theoretical performance is derived by means of equilibrium point analysis (EPA) and is examined by extensive computer simulation     

Bit-to-bit error dependence in slotted DS/SSMA packet systems withrandom 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     

Maximum throughput of FHSS multiple-access networks using MFSK modulation

Optimum values for the modulation order M, code rate r, and the number of frequency-hop slots q maximizing the network throughput are obtained based on simulations for frequency-hopped spread-spectrum multiple-access networks, where L Q-ary Reed-Solomon (RS) code symbols are transmitted per hop, and each Q-ary RS code symbol is transmitted using log/sub M/Q M-ary frequency-shift-keying-modulated signals. Network throughput is evaluated under additive white Gaussian noise and Rayleigh fading channels. For the case when the received RS symbol is not interfered by multiple-access interference (MAI), a closed-form expression for the symbol-error probability is derived, and for the case when the symbol is interfered by MAI, simulated symbol-error probabilities are used. It is shown that the optimum M is four or eight, irrespective of the channel environment and the number of users. The optimum code rate is determined primarily based on the channel environment and does not show much dependence on M or Q. It is also shown that for the case of synchronous hopping under Rayleigh fading at high signal-to-noise ratios, the difference in instantaneous power among the interfering users significantly improves the performance, compared with the case when there is no fading. We also consider the case when the receiver erases the symbols that are interfered and compare the performance with the case of the hard decisions receiver.     

Comments on `Packet error probabilities in frequency-hoppedspread-spectrum packet radio networks-memoryless frequency-hoppingpatterns 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     

Performance of a type-II hybrid ARQ protocol in slotted DS-SSMApacket radio systems

The application of a type-II hybrid ARQ protocol in a slotted direct-sequence spread-spectrum multiple-access (DS-SSMA) packet radio system is investigated. Both the static performance and the dynamic performance of such a system are analyzed. In the physical layer, packet error and packet success probabilities are computed using the improved Gaussian approximation technique, which accounts for the bit-to-bit error dependence within a packet. In the data-link layer, two-dimensional Markov chains are employed to model the system dynamics. Based on this model, the performance of the type-II hybrid ARQ protocol is upper and lower bounded by considering, respectively, a superior scheme and an inferior scheme. Steady state throughput and delay performances of the two bounding schemes are obtained. Moreover, it is shown that for each fixed input load, there is an optimal retransmission probability under the finite user population assumption. Bounds on this optimal retransmission probability are also given     

A technique to improve the performance of serial, matched-filter acquisition in direct-sequence spread-spectrum packet radio communications

In this paper, we examine a simple method to improve the performance of serial, matched-filter acquisition in direct-sequence spread-spectrum packet radio communications. Each packet transmission includes an acquisition preamble, and the preamble sequence is changed at the boundaries of predefined time epochs based on a pseudorandom sequence generator. It is shown in previous work that the presence of an intermediate-frequency filter and the characteristics of the automatic gain-control subsystem lead to a probability of not acquiring that is a nonmonotonic function of the signal-to-noise ratio if the acquisition algorithm uses a threshold-crossing detector with a fixed threshold. The acquisition algorithm presented in this paper employs an estimator to adaptively select the acquisition threshold for each test statistic. It is shown that this technique reduces the severity of the nonmonotonicity and substantially improves the acquisition performance.     

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 comparison of different spread-spectrum signalingschemes for cellular mobile radio networks

Different spread-spectrum signaling schemes in a cellular mobile radio network are compared in terms of throughput and packet error probability. Bounds on the bit and packet error probabilities are derived for data modulation schemes with binary phase shift keying with noncoherent demodulation. Reed-Solomon coding is employed for error-correction purposes. In all cases, the effect of varying interference power (according to some inverse power of distance) of the desired signal, of the interfering signals, and of Rayleigh nonselective channel fading is accurately taken into account. The throughput in the mobile-to-base transmission mode is evaluated for the above data modulation, demodulation, and forward-error-control coding schemes. The comparison shows that, under the varying interference power model, the frequency-hopped scheme performs best among all schemes with the same bandwidth. Power control mechanisms are required to improve the performance of direct-sequence systems     

Accurate DS-CDMA Packet-Error Rate Analysis in Rayleigh Fading

We present new packet-error rate (PER) analysis for both slotted and unslotted direct-sequence spread-spectrum packet communication systems in a slow Rayleigh fading environment. Based on the accurate improved Gaussian approximation, we derive closed-form expressions for the cumulative probability distribution function of the signal-to-interference-plus-noise ratio in binary phase-shift keying (PSK), quadratic PSK, and differential PSK-based code-division multiple-access (CDMA) systems having different types of chip waveforms including bandwidth-efficient waveforms. This leads to new accurate unified expressions for the PERs that account for bit-to-bit error dependence, which are valid for packets with unequal power levels. These new results facilitate accurate computation of the throughput performance of CDMA-based ALOHA local radio networks     

The probability of multiple correct packet reception in codedsynchronous frequency-hopped spread-spectrum networks

We present a computationally efficient method of evaluating the probability of multiple correct packet reception in coded synchronous frequency-hopped spread-spectrum (FHSS) networks. We show that the approximation using the independent receiver operation assumption (IROA), which has been frequently employed in the literature without rigorous validation, produces reasonable results in most network load conditions when compared to the exact computations derived from our proposed method. Specifically, the expected value of the absolute error was in the range of 0.0055%-18.21% in the investigated scenarios