• Journal of Internet Computing and Services
• /
• v.13 no.1
• /
• pp.7-14
• /
• 2012

In this paper, performance of IEEE 802.11 carrier-sense multiple access with collision-avoidance (CSMA/CA) protocols in saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the performance of IEEE 802.11 is analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the probability of detection is concluded as a dominant factor for the performance of IEEE 802.11.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.6 no.4
• /
• pp.989-1005
• /
• 2012

In this paper, throughput of IEEE 802.11 carrier-sense multiple access (CSMA) with collision-avoidance (CA) protocols in non-saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the utilization of IEEE 802.11 analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the choice of the best probability detection while maintaining probability of false alarm is less than 0.5 is a key factor for maximizing utilization of IEEE 802.11.

• Proceedings of the IEEK Conference
• /
• 2003.07a
• /
• pp.198-201
• /
• 2003

In this paper, we analyze high-rate orthogonal frequency division multiplexing(OFDM) system using time switched time diversity(TSTD) method based on IEEE 802.11a. First, we modeled the transmitter and receiver of OFDM system based on IEEE 802.11a. Then, we applied the TSTD to OFDM system. Finally we analyzed the performance of OFDM system using TSTD method by simulation over the 5GHz realistic channel model, where channel coding and channel equalizer over multipath environment are also applied.

• Journal of Advanced Navigation Technology
• /
• v.13 no.2
• /
• pp.214-223
• /
• 2009

In this paper, we analysed and simulated the high speed mobile wireless channel for IEEE802.11p WAVE/DSRC standard draft. IEEE802.11p working group measured and suggested 6 channel model for WAVE/DSRC systems which is used for vehicle to vehicle or vehicle to infra communication. However, the models only provides numerical model, it did not provide Computer based software simulation model. So it can not be used directly for performance estimation of WAVE system. In this paper we suggested simulation technique of WAVE channel simulation which is developed S/W based WAVE channnel simulator. The simulation results for PSD, LCR, and AFD are also obtained, which can be used for performance estimation of IEEE802.11p based vehicular communication system.

• Journal of the Korea Society of Computer and Information
• /
• v.10 no.4 s.36
• /
• pp.249-257
• /
• 2005

A Markov model for the IEEE 802.11 standard which is the most widely deployed wireless LAN protocol, is designed and the channel throughput is evaluated. The DCF of 802.11, which is based on CSMA/CA protocol, coordinates transmissions onto the shared communication channel. In this paper, under a finite load traffic condition and the assumption of packet loss after the final backoff stage. We present an algorithm to find the transmission probability and derive the formula for the channel throughput. The proposed model is validated through simulation and is compared with the case without packet losses.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.1A
• /
• pp.73-81
• /
• 2011

IEEE 802.11 PHY and MAC layer provide multiple channels and data rates. To improve the performance of IEEE 802.11 multi-radio ad hoc networks, it is required to utilize available channels and data rates efficiently. However, in IEEE 802.11 multi-rate networks, the rate anomaly (RA) problem occurs that the network performance is severely degraded as low-rate links affect high-rate links. Hence, in this paper, we propose a model-based rate separation (MRS) algorithm that uses multiple channels to separate different data rate links so that the RA problem is mitigated. MRS algorithm utilizes an existing throughput model that estimates the throughput of IEEE 802.11 single-hop networks to separate low-rate links and high-rate links. Through simulations, we demonstrate that the MRS algorithm shows improved network performance compared with existing algorithms in multi-radio ad hoc networks.

• Journal of Advanced Navigation Technology
• /
• v.13 no.6
• /
• pp.943-949
• /
• 2009

In this paper, the 5.9GHz WAVE(Wireless Access in Vehicular Environments) channel modeling is used by the Jakes channel model for the suitability of the fast wireless channel fluctuation. The performance analysed the fading signal constellation and the spectrum in the IEEE 802.11p spectrum mask, the Doppler effect, the modulation scheme. In addition, the vehicular speed, exactly the performance analysis the WAVE communication systems follow the Doppler effect.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.8 no.3
• /
• pp.556-562
• /
• 2007

In this paper we propose a new method which adjusts the collision resolution depending on busy status of the channel to improve performance of IEEE 802.11 DCF. This scheme reduces the number of collisions in wireless channel by decreasing the amount of movements of each station's backoff stage based on busy event count and the one stage backoff model. Through simulation, we compared the performance of our scheme with that of DCF, ADCF and SD.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.6 no.2
• /
• pp.683-701
• /
• 2012

IEEE 802.11 standard has achieved huge success in the past decade and is still under development to provide higher physical data rate and better quality of service (QoS). An important problem for the development and optimization of IEEE 802.11 networks is the modeling of the MAC layer channel access protocol. Although there are already many theoretic analysis for the 802.11 MAC protocol in the literature, most of the models focus on the saturated traffic and assume infinite buffer at the MAC layer. In this paper we develop a unified analytical model for IEEE 802.11 MAC protocol in ad hoc networks. The impacts of channel access parameters, traffic rate and buffer size at the MAC layer are modeled with the assistance of a generalized Markov chain and an M/G/1/K queue model. The performance of throughput, packet delivery delay and dropping probability can be achieved. Extensive simulations show the analytical model is highly accurate. From the analytical model it is shown that for practical buffer configuration (e.g. buffer size larger than one), we can maximize the total throughput and reduce the packet blocking probability (due to limited buffer size) and the average queuing delay to zero by effectively controlling the offered load. The average MAC layer service delay as well as its standard deviation, is also much lower than that in saturated conditions and has an upper bound. It is also observed that the optimal load is very close to the maximum achievable throughput regardless of the number of stations or buffer size. Moreover, the model is scalable for performance analysis of 802.11e in unsaturated conditions and 802.11 ad hoc networks with heterogenous traffic flows.

• Journal of Advanced Navigation Technology
• /
• v.6 no.3
• /
• pp.203-210
• /
• 2002

In this paper, the BER performance of IEEE 802.11a OFDM WLAN system is obtained by simulation and it is shown that the proposed modified channel estimation algorithm improves the channel estimation performance of the system. The wireless channel used in channel simulation includes AWGN and delay spread channel implemented by TDL model. At first, the performance of OFDM WLAN system according to data rate and coding rate defined in standard is evaluated in AWGN channel. Then, imperfect channel estimation in indoor wireless channel is considered. After the performance of conventional channel estimation scheme using only two long training symbols is evaluated, and that of proposed modified channel estimation scheme using additional 8 short training symbol is compared with it. From the simulation results, it is shown that modified channel estimation scheme provides reduced channel estimation error and improves the channel estimation performance due to noise averaging effect with the same preamble format as defined in specification.