• ETRI Journal
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• 제33권2호
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• pp.184-193
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• 2011

Tailored for wireless local area networks, the present paper proposes a cross-layer resource allocation scheme for multiple-input multiple-output orthogonal frequency-division multiplexing systems. Our cross-layer resource allocation scheme consists of three stages. Firstly, the condition of sharing the subchannel by more than one user is studied. Secondly, the subchannel allocation policy which depends on the data packets' lengths and the admissible combination of users per subchannel is proposed. Finally, the bits and corresponding power are allocated to users based on a greedy algorithm and the data packets' lengths. The analysis and simulation results demonstrate that our proposed scheme not only achieves significant improvement in system throughput and average packet delay compared with conventional schemes but also has low computational complexity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권11호
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• pp.2636-2656
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• 2013

To improve the cooperative efficiency of node cooperation and multiple access performance for multihop wireless networks, a priority-differentiated cooperative medium access control protocol with contention resolution (CRP-CMAC) is proposed. In the protocol, the helper selection process is divided into the priority differentiation phase and the contention resolution phase for the helpers with the same priority. A higher priority helper can choose an earlier minislot in the priority differentiation phase to send a busy tone. As a result, the protocol promptly selects all the highest priority helpers. The contention resolution phase of the same priority helpers consists of k round contention resolution procedures. The helpers that had sent the first busy tone and are now sending the longest busy tone can continue to the next round, and then the other helpers that sense the busy tone withdraw from the contention. Therefore, it can select the unique best helper from the highest priority helpers with high probability. A packet piggyback mechanism is also adopted to make the high data rate helper with packet to send transmit its data packets to its recipient without reservation. It can significantly decrease the reservation overhead and effectively improve the cooperation efficiency and channel utilization. Simulation results show that the maximum throughput of CRP-CMAC is 74%, 36.1% and 15% higher than those of the 802.11 DCF, CoopMACA and 2rcMAC protocols in a wireless local area network (WLAN) environment, and 82.6%, 37.6% and 46.3% higher in an ad hoc network environment, respectively.

• 한국통신학회논문지
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• 제31권5B호
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• pp.365-377
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• 2006

매체공유기반 통신시스템은 매체접근제어 과정에서 단말기의 채널 점유 제약 조건에 따라 크게 완전매체공유 시스템과 불완전매체 공유 시스템으로 구분할 수 있다. 본 논문에서는 불완전매체공유 시스템의 채널활용효율을 향상시키기 위한 분산식 매체접근제어기법을 제안한다. 제안하는 매체접근제어기법은 IEEE 802.11 무선랜의 CSMA/CA 기법을 확장한 방법으로써 임의 지연 시간을(random backoff time) 채널에 대해 개별적, 집합적, 큐(queue)에 대해 개별적으로 적용함으로써 크게 3가지 형태로 제시되었다. 모의실험 결과 성능측면에서는 큐에 대해 개별적으로 임의 지연시간을 적용하였을 때 상대적으로 우월한 성능을 보였다. 또한 복잡도 측면에서는 채널에 대하여 집합적으로 임의 지연시간을 적용했을 때 상대적으로 낮은 복잡도를 보였다. 임의 지연시간을 분할된 채널에 대해 개별적으로 적용하는 방식은 성능과 연산복잡도의 trade-off관계에 있어서 앞서 제시된 방식들보다 우위에 있음을 보이고 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권8호
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• pp.3862-3888
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• 2017

In high diversity node situation, single-channel MAC protocols suffer from many collisions. To solve this problem, the research of multichannel MAC protocol has become a hotspot. And the cyclic quorum-based multichannel (CQM) MAC protocol outperformed others owing to its high frequency utilization. In addition, it can avoid the bottleneck that others suffered from and can be easily realized with only one transceiver. To obtain the accurate performance of CQM MAC protocol, a Markov chain model, which combines the channel hopping strategy of CQM protocol and IEEE 802.11 distributed coordination function (DCF), is proposed. The metrics (throughput and average packet transmission delay) are calculated in performance analysis, with respect to node number, packet rate, channel slot length and channel number. The results of numerical analysis show that the optimal performance of CQM protocol can be obtained in saturation bound situation. And then we obtain the saturation bound of CQM system by bird swarm algorithm (BSA). Finally, the Markov chain model and saturation bound are verified by Qualnet platform. And the simulation results show that the analytic and simulation results match very well.