We analyze performance of slotted ALOHA systems with energy harvesting nodes and retry limit.We assume that the capacities of data and energy buffer at a node are one packet and E packets, respectively, and that one data packet transmission consumes one energy packet.The data and the energy packet arrival processes are modeled by independent Bernoulli processes.Under these assumptions, we develop a node-centric two-dimensional discrete time Markov chain model.Based on the equilibrium point analysis, we derive the fixed point equation with respect to the ratio of nodes transmitting a data packet.The accuracy of numerical results derived from the fixed point equation is verified by computer simulation.The numerical results indicate that throughput, the offered traffic and the discard probability roughly depend on the minimum of the data packet generation probability and the energy packet generation probability.This work was partly supported by Japan Society for the Promotion of Science

This paper proposes bidirectional packet aggregation and coding (BiPAC), a packet mixing technique which jointly applies packet aggregation and network coding in order to increase the number of supportable VoIP sessions in wireless multi-hop networks. BiPAC applies network coding for aggregated VoIP packets by exploiting bidirectional nature of VoIP sessions, and largely reduces the required protocol overhead for transmitting short VoIP packets. We design BiPAC and related protocols so that the operations of aggregation and coding are well-integrated while satisfying the required quality of service by VoIP transmission, such as delay and packet loss rate. Our computer simulation results show that BiPAC can increase the number of supportable VoIP sessions maximum by around 70% as compared with the case when the packet aggregation alone is used, and 450% in comparison to the transmission without aggregation/coding. We also implement BiPAC in a wireless testbed, and run experiments in an actual indoor environment. Our experimental results show that BiPAC is a practical and efficient forwarding method, which can be implemented into the current mesh hardware and network stack.

We analytically compare the performance of imperfectly symbol- and bit-interleaved block codes over GF(2/sup m/) on a first-order Markovian channel in terms of the error probability of a received word. The analytical method developed in Sakakibara (2000) is extended, so that binary transmission of block codes over GF(2/sup m/) can be incorporated with the assumption of negligible probabilities of decoding error. Expressions are derived for two decoding strategies; independent bounded-distance (IBD) decoding and error-forecasting (EF) decoding. In the IBD decoding, channel errors up to half of the minimum distance can be decoded in each received word. On the other hand, combining an erasures-and-errors decoding algorithm, more errors may be corrected in the EF decoding. The derived expressions are examined on two typical classes of two-state Markovian channels. Numerical results indicate that a combination of symbol-interleaving and the EF decoding offers the best performance even for imperfect interleaving. This can compensate for the superiority of perfect symbol-interleaving to perfect bit-interleaving addressed by Wicker (1992). It is also found that the optimum depths of symbol- and bit-interleaver is approximately given by 2b and 4b, respectively, where b is the average length of burst errors in bits.

The combinatorial effect of an exponential backoff scheme and retransmission cutoff on the stability of frequency-hopping slotted ALOHA systems with finite population is investigated in terms of the catastrophe theory. In the systems, the packet retransmission probabilities are geometrically distributed with respect to the number of experienced unsuccessful transmissions and a packet will be discarded after a certain number of unsuccessful transmissions. Expressions which should be satisfied at equilibrium points are first derived. Then, the cusp point and the bifurcation sets are numerically evaluated. Finally, we visualize how the exponential backoff scheme and retransmission cutoff effect depends on the bistable region. Numerical results show that the exponential backoff scheme can mitigate bistable behavior of the system with finite population. However, it is also revealed that there is asymptotically no effect of the exponential backoff scheme on the stability of the system with infinite population.

We propose an admission control for slow-frequency-hopped slotted random access networks. The proposed scheme delays new packet transmission until the number of backlogged users decreases to the threshold or less. Performance of the proposed protocol is evaluated with a two-dimensional Markov chain for systems with finite number of users in terms of throughput efficiency and the average transmission delay. Numerical results show that the proposed protocol can achieve better performance, compared to the conventional frequency-hopped slotted ALOHA. The optimum value of the threshold is also numerically derived.

This paper investigates the performance of the error-forecasting decoding for an interleaved block code on Gilbert-Elliott channels in terms of the word-error probability, which is the sum of the decoder error and failure probabilities. We derive expressions by constructing several Markov chains, starting from a two-state Markov chain of the Gilbert-Elliott channel model. The derived formulas are examined for an interleaved Reed-Solomon code on solid-density and moderate-density burst error channels. Numerical results indicate that the error-forecasting decoding can significantly improve the performance, particularly on solid-density burst error channels. The optimal depth of interleaving for the error-forecasting decoding is also numerically evaluated.

We discuss a lower bound on the minimum distance of a q-ary image of q/sup m/-ary cyclic code, based on its concatenated structure due to Jensen (see ibid., vol.31, no.6, p.788-93, 1985) and Seguin (see ibid., vol.41, no.2, p.387-99, 1995). An explicit estimate for the minimum distance of the outer codes, which is analogous to the BCH bound, is derived. Complete lists of the values obtained from the lower hound are given for binary images of 2/sup 5/-ary and 2/sup 6/-ary Reed-Solomon codes.

An efficient multicast hybrid ARQ scheme is proposed by incorporating the generalized minimum distance (GRID) decoding of maximum distance separable (MDS) codes with Metzner's (1984) scheme. Erroneous frames are stored in the receiver buffer and recovered after receiving one or more redundant frames. The throughput and the average transmission delay of the proposed scheme are analyzed on memoryless symmetric channels. The proposed scheme can circumvent the degradation of the throughput due to an increase of the number of receivers, which is the most serious defect in the conventional multicast ARQ schemes, at the expense of the transmission delay.