Maximum Throughput Efficiency Research Articles

Adaptive coalition with Kullback‐Leibler divergence for cooperative spectrum sensing (KLDCSS) in cognitive radio networks

SummaryEffective, reliable, and rapid spectrum sensing in concordance with maximum throughput efficiency is necessary at the cognitive radio network to maximize the network's utilization. An adaptive coalition using Kullback–Leibler divergence (KLD)‐based cooperative spectrum sensing scheme (KLDCSS) with a nominal sensing time to optimize the spectral efficiency is presented in this paper. In a coalition‐based spectrum sensing scheme, cooperating secondary users (SUs) are allocated to different coalitions to sense different Primary User (PU) channels. The same cognitive users allocated to sense the primary user channels are allotted to detect in different sensing phases. In the proposed sensing scheme, the cooperating SUs are adaptively allocated to different coalitions to maximize the throughput efficiency. Collaborating cognitive users with a standard signal‐to‐noise ratio and distinct energy levels that are characterized by the localized probabilities of detection and false alarm is considered. An adaptive coalition and user allocation algorithm are proposed to optimize the average opportunistic throughput and diminish the sensing overhead. The expression for throughput efficiency in terms of average throughput and sensing accuracy is derived. In this scheme, the SU computes the log‐likelihood ratio (LLR) from the acquired sample and forwards the same to the fusion center. The fusion center then accumulates the LLR values computed by the SU to estimate the likelihood of spectrum availability. Simulation results highlighting the competitive edge of the proposed scheme, with higher throughput efficiency over various numbers of SUs, coalitions, and signal‐to‐noise ratios, are presented.

Adaptive Time-Switching Based Energy Harvesting Relaying Protocols

Considering a dual-hop energy-harvesting (EH) relaying system, this paper advocates novel relaying protocols based on adaptive time-switching (TS) for amplify-and-forward and decode-and-forward modes, respectively. The optimal TS factor is first studied, which is adaptively adjusted based on the dual-hop channel state information (CSI), accumulated energy, and threshold signal-to-noise ratio (SNR), to achieve the maximum throughput efficiency per block. To reduce the CSI overhead at the EH relay, a low-complexity TS factor design is presented, which only needs single-hop CSI to determine the TS factor. Theoretical results show that, in comparison with the conventional solutions, the proposed optimal/low-complexity TS factor can achieve higher limiting throughput efficiency for sufficiently small threshold SNR. As the threshold SNR approaches infinity, the throughput efficiency of the proposed optimal/low-complexity TS factor tends to zero in a much slower pace than that of the conventional solutions. Simulation results are presented to corroborate the proposed methodology.

Successive Interference Cancellation With Feedback for Random Access Networks

We consider a random access network in which $K$ nodes wish to send independent packets to an access point (AP). In this letter, a novel method of feedback construction and an adaptive retransmission protocol of collided packets are proposed, which enable efficient successive interference cancellation at the AP. We show that the optimal throughput efficiency of one is achievable by only exploiting $\log K$ bits of feedback from the AP to $K$ nodes, while the maximum throughput efficiency of slotted ALOHA is known to be $e^{-1}\approx 0.37$ for large $K$ . Note that the proposed technique achieves the optimal throughput efficiency for any finite $K$ , while the conventional techniques asymptotically achieve the optimal throughput efficiency only when $K$ tends to infinity.

All-Optical WDM Cross-Connect Meshed-Ring Communications Networks

We introduce a meshed ring communications network which employs cross-connect switches. The crossconnect switches can be implemented as wavelength routers resulting in WDM networks, or as ATM Virtual Path (VP) switches leading to ATM compatible network systems. We show in the paper that this network architecture results in a significant increase in throughput performance in comparison with (SDHISONET) ring networks. For a certain class of meshed rings, under a uniform traffic matrix, we derive the optimal topology which achieves maximum throughput efficiency. Using such a topology, we obtain upper and lower bounds on the number of wavelengths required to achieve that efficiency level. The network is divided into (overlapping) communities of nodes. Each community is assigned a wavelength and a subnetwork (identified as a wavelength graph). Each pair of nodes in a community can communicate across the associated wavelength graph. Wavelength graphs (subnets) are constructed to demonstrate the implementation of the routing scheme using the number of wavelengths that is equal to the derived upper bound. For practical implementation reasons, we investigate the performance of networks which employ a reduced number of wavelengths. We show that by modifying the topological layout of the meshed ring network, we can reduce substantially the number of required wavelengths, while incurring just a modest reduction in throughput efficiency.

Design principles and performance analysis of SSCOP

The Service Specific Connection Oriented Protocol (SASCOP) has been approved recently as a new B-ISDN ATM Adaptation Layer (AAL) protocol standard, initially for use in the Signaling ATM Adaptation Layer (SAAL), but also for support of certain types of use data transfer. SSCOP is a new type of protocol, embodying several design principles for high speed link and transport layer protocols. In this paper, the basic operation of SSCOP is described and the SSCOP design is compared with other similar protocols. Next, the relationships between key protocol parameters (protocol window, control message transmission interval) and maximum achievable throughput effieiency are explored. In particular, approximate performance equations are derived for predicting the maximum throughput efficiency of SSCOP basedon the selected environment and parameter eettings. The equations can be used to determine how much buffer capacity and/or what protocol timer settings allow SSCOP to operate at high performance. The analytical results are confirmed through comparison with simulation results. In addition, simulation results illustrate the high throughput performance achievable when using SSCOP in a highly errored or loosy environment.

Optimal Control of Arrivals to Token Ring Networks with Exhaustive Service Discipline

The optimal control of arrivals to a two-station token ring network is analyzed in this paper. By adopting a maximum system throughput under a system time-delay constraint optimality criterion, we study a network optimality problem with the assumption that both stations have global information (i.e., the number of packets at each station). The controlled arrivals are assumed to be state-dependent Poisson streams and have exponentially distributed service time. The optimality problem will be formulated using dynamic programming with a convex cost function. Combining with duality theory, we then show that the optimal control is almost bang-bang and in the special case when both queues have the same service rate and sufficiently large buffers, the optimal control is further shown to be switchover. A nonlinear program is used to numerically determine the optimal local control for the purpose of comparison. The results obtained under global and local information can be used to provide a measure of the tradeoff between maximum throughput efficiency and protocol complexity. Numerical examples illustrating the theoretical results are also provided.

Performance of Hybrid Error Control Schemes of Satellite Channels

The effectiveness of hybrid error control schemes involving forward error correction (FEC) and automatic repeat request (ARQ) is examined for satellite channels. The principal features of the channel are: large round-trip transmission delay due to the satellite link, and burst errors introduced by the terrestrial links that connect the users to the satellite link. The performance is estimated for two channels described by Fritchman's simple partitioned finite-state Markov model, and is compared to that obtainable if the channel is considered as a binary symmetric channel of the same bit error probability. Results show that the hybrid schemes offer substantial improvement over ARQ and FEC, and that an optimum exists for the number of errors corrected to obtain maximum throughput efficiency.