Throughput Of Distributed Coordination Function Research Articles

A Rapidly Adaptive Collision Backoff Algorithm for Improving the Throughput in WLANs

In the 802.11 protocol, the fundamental medium access mechanism is called Distributed Coordination Function (DCF). In DCF, before making any transmission attempt, the nodes count down a timer with a value randomly selected from the Contention Window (CW) size. If the transmitted packet is involved in a collision, the node increases the CW size in an attempt to reduce the collision rate. Conversely, if the packet is transmitted successfully, the node reduces the CW size in order to increase the frequency of the transmission attempts. The growth or reduction in the CW size has a critical effect on the network performance. Several backoff algorithms have been proposed to improve the system throughput. However, none of these methods enable the system to approach the theoretical maximum throughput possible under DCF. Accordingly, this study proposes the Rapidly Adaptive Collision Backoff (RACB) algorithm, in which the CW size is adjusted dynamically based on the collision rate, as analyzed by a mathematical model. Notably, RACB requires no knowledge of the number of nodes in the wireless network and is applicable to both lightly loaded and heavily loaded networks. The numerical results show that, by adjusting the CW size such that the collision rate is maintained at a value close to 0.1, RACB enables the system throughput to approach the maximum DCF throughput in wireless environments containing any number of nodes.

A GA-based simulation system for WMNs: comparison analysis for different number of flows, client distributions, DCF and EDCA functions

In this paper, we compare the performance of Distributed Coordination Function (DCF) and Enhanced Distributed Channel Access (EDCA) for normal and uniform distributions of mesh clients considering two Wireless Mesh Network (WMN) architectures. As evaluation metrics, we consider throughput, delay, jitter and fairness index metrics. For simulations, we used WMN-GA simulation system, ns-3 and Optimized Link State Routing. The simulation results show that for normal distribution, the throughput of I/B WMN is higher than Hybrid WMN architecture. For uniform distribution, in case of I/B WMN, the throughput of EDCA is a little bit higher than Hybrid WMN. However, for Hybrid WMN, the throughput of DCF is higher than EDCA. For normal distribution, the delay and jitter of Hybrid WMN are lower compared with I/B WMN. For uniform distribution, the delay and jitter of both architectures are almost the same. However, in the case of DCF for 20 flows, the delay and jitter of I/B WMN are lower compared with Hybrid WMN. For I/B architecture, in case of normal distribution the fairness index of DCF is higher than EDCA. However, for Hybrid WMN, the fairness index of EDCA is higher than DCF. For uniform distribution, the fairness index of few flows is higher than others for both WMN architectures.

IEEE 802.11ac/ad 무선 LAN의 적응형 MCS 구현 연구

This paper analyzes the rate adaptation scheme and suggests applicable strategy of the MCS(Modulation and Coding Scheme) for improving DCF throughput in the IEEE 802.11ad and 802.11ad wireless LAN. IEEE 802.11ac and 802.11ad wireless LAN provide MCS technique that dynamically adjusts modulation level and code rate to the time-varying channel conditions in order to obtain considerably high data rates. But these standards did not provide rate adaptation algorithm, so this paper surveyes rate adaptation algorithm and suggests MCS scheme applied to IEEE 802.11ac and 802.11ad wireless LAN. Specially A MAC(Medium Access Control) layer throughput is evaluated over error-prone channel in the IEEE 802.11ac-based wireless LAN. In this evaluation, DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme are used. Using theoretical analysis method, the MAC saturation throughput is evaluated with the PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables.

DCF Throughput Analysis of IEEE 802.11a/g/n-based Mobile LAN over Correlated Fading Channel

This paper explores a MAC (Medium Access Control) layer throughput with DCF (Distributed Coordination Function) protocol in the IEEE 802.11a/g/n-based mobile LAN. It is evaluated in Rayleigh fading wireless channel, using theoretical analysis method. The DCF throughput performance is analyzed by using the number of stations with both variable payload size and mobile speed on the condition that fading margin and transmission probability are fixed. In the IEEE 802.11n, A-MSDU (MAC Service Data Unit Aggregation) scheme is considered and number of subframe is used as the variable parameter. It is identified that MAC efficiency of IEEE 802.11n is the best out of four schemes.

Throughput analysis of IEEE 802.11 WLANs with Automatic Rate Fallback in a lossy channel

This paper presents a new two-step mathematical model which analyzes the throughput of the IEEE 802.11 distributed coordination function (DCF) with the automatic rate fallback (ARF) rate adaptation algorithm. First, the ARF algorithm is modeled as a discrete-time Markov chain and, from the Markov chain, the station distribution among physical rates is obtained. Then, it is fed to the DCF throughput model which takes the backoff mechanism into account. This two-step approach simplifies the overall model by separating the ARF algorithm and the backoff mechanism in modeling.

무선 LAN에서 이상 및 페이딩 채널 환경의 DCF 처리율 비교 분석

본 논문에서는 IEEE 802.11a 무선 LAN의 이상적인 채널 환경과 페이딩 채널 환경에서 패킷의 페이로드 크기에 따른 MAC(Medium Access Control) 계층의 CSMA/CA(Carrier Sense Multiple Access/Collision Avoidance) 기반 DCF(Distributed Coordination Function) 처리율을 비교 분석하였다. 이상적인 채널 환경인 경우 에러가 없는 채널을 의미하고, 임의의 전송 주기 동안 패킷을 전송하는 단말이 1개만 존재하며, 다른 단말은 패킷을 수신한 후 응답한다고 가정한다. 페이딩 채널 환경인 경우 채널상에서 비트 에러는 랜덤하게 발생되며, 단말수 n은 고정되고, 각각의 단말은 항상 전송 패킷을 가지고 있는 포화 조건(saturation condition) 하에서 동작된다고 한다. IEEE 802.11a 무선 LAN의 처리율을 구하기 위해 기존 연구에서는 주로 이상적인 채널 환경을 가정하여 최대 처리율을 구하였는데, 실제의 통신 환경은 페이딩 패널이므로 본 연구에서는 <TEX>$E_b/N_o$</TEX>를 25 dB, 부 채널에서 직접 수신된 신호와 산란되어 수신된 신호의 전력비 <TEX>$\xi$</TEX>는 복합 Rayleigh/Ricean 페이딩을 고려하여 6으로 정하였다. 분석 결과, 이상적인 채널 환경에서의 처리율에 비교하여 페이딩 채널 환경에서의 처리율이 모든 페이로드 크기에서 더 작아진다는 것을 알 수 있으며, 전송율이 증가할수록 이상적인 채널의 최대 처리율에 대한 페이딩 채널의 포화 처리율의 감소 비율이 더 커진다는 것도 알 수 있다. This paper explores the throughput performance of CSMA/CA-based DCF protocol over both ideal channels and fading channels with payload size at the MAC layer in the 802.11a wireless LAN. In the ideal channel, there are no errors and at the transmission cycle there is one and only one active station which always has a packet to send and other stations can only accept packets and provide acknowledgements. In the fading channel, bit errors appear in the channel randomly and the number of stations is assumed to be fixed. And each station always has packets for transmission. In other words, we operate in saturation conditions. Up to now conventional research work about DCF throughput analysis of IEEE 802.11 a wireless LAN has been done over the ideal channel, but this paper is done over the Rayleigh/Ricean fading channel. So, the ratio of received average energy per bit-to-noise power spectral density <TEX>$E_b/N_o$</TEX> is set to 25 dB and the ratio of direct-to-diffuse signal power in each sub-channel <TEX>$\xi$</TEX> is set to 6 for combined Rayleigh/Ricean fading channel. In conclusion, it is shown that the saturation throughput is always less than the maximum throughput at all the payload size and the higher the transmission rate be, the higher the decreasing rate of saturation throughput compared to the maximum throughput be.

Performance modelling and evaluation of IEEE 802.11 distributed coordination function in multihop wireless networks

Initially designed for WLAN's, IEEE 802.11 medium access control (MAC) has also been widely used in the research of multihop wireless networks. The core MAC technique of IEEE 802.11 is called distributed coordination function (DCF). DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme combined with binary exponential backoff (BEB). In this paper we present an analytical model to derive the saturation throughput of DCF in multihop wireless networks with nodes randomly placed according to a two-dimensional Poisson distribution. The proposed framework applies to both packet transmission schemes employed by DCF, namely, the basic access and the RTS/CTS access mechanisms. By means of the proposed model, we evaluate throughput performance of DCF in multihop wireless networks. Our model indicates that the RTS/CTS access method with the default parameters operates in a region almost optimal in terms of saturation throughput.

Performance analysis of the IEEE 802.11 distributed coordination function

The IEEE has standardized the 802.11 protocol for wireless local area networks. The primary medium access control (MAC) technique of 802.11 is called the distributed coordination function (DCF). The DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. This paper provides a simple, but nevertheless extremely accurate, analytical model to compute the 802.11 DCF throughput, in the assumption of finite number of terminals and ideal channel conditions. The proposed analysis applies to both the packet transmission schemes employed by DCF, namely, the basic access and the RTS/CTS access mechanisms. In addition, it also applies to a combination of the two schemes, in which packets longer than a given threshold are transmitted according to the RTS/CTS mechanism. By means of the proposed model, we provide an extensive throughput performance evaluation of both access mechanisms of the 802.11 protocol.