Hiroki Sugimoto

Rate Adaptive Reliable Multicast MAC Protocol for WLANs

IEEE 802.11b standard provides 1, 2, 5.5, 11 Mbps data rates. These data rates can be made possible by using different modulation techniques: DBPSK, DQPSK, CCK5.5 and CCK11 respectively. Rate adaptation is the process of dynamically selecting a proper modulation scheme depending on channel conditions in order to improve total throughput. Current rate adaptation protocols deal with unicast links rather than multicast. Channel conditions can be estimated by measuring the received signal strength (RSS) of a feedback message (CTS, ACK). However, IEEE 802.11 standard does not provide feedback messages for MAC layer recovery on multicast frames. This is due to collisions which may occur to simultaneous feedback messages from multicast group members. Therefore, in order to rate adapt multicast, a reliable multicast MAC protocol has to be introduced. In this paper, we propose a protocol which provides multicast reliability to WLANs and enhances its throughput by using rate adaptation. Further, we evaluate our protocol by throughput analysis and computer simulation. Simulation results suggest that our protocol performs better than a related/existing protocol in both throughput as well as reliability performances

A Rate Adaptive Multicast Protocol for Providing MAC Layer Reliability in WLANs

IEEE802.11b standard provides 1, 2, 5.5, 11 Mbps data rates. These data rates can be made possible by using different modulation techniques: DBPSK, DQPSK, CCK5.5 and CCK11 respectively. Rate adaptation is the process of dynamically selecting a proper modulation scheme depending on channel conditions in order to improve total throughput. Current rate adaptation protocols deal with unicast links rather than multicast. Measuring the received Signal Strength (RSS) of a feedback message (CTS, ACK) to estimate the receivers link condition, can be one way to do this. A receiver may send its channel condition information to the sender allowing it to adapt its data rate for the following transmission. IEEE802.11 standard however, does not provide feedback messages for MAC layer recovery on multicast frames. This is due to collisions occurring if multicast group members simultaneously initiate a feedback message. Therefore, in order to link adapt multicast, a reliable multicast MAC protocol has to be introduced. In this paper, we propose a Rate Adaptive Multicast (RAM) protocol which provides reliability to WLANs and enhances its throughput by using Rate Adaptation. Further, we evaluate our protocol by throughput analysis and computer simulation. Simulation results suggest that our protocol performs better than related/existing protocols in both throughput as well as reliability.

Higher data rate wireless LAN system based on OFDM

In this paper, the performance of a higher data rater OFDM system based on IEEE802.11a is described. The performance of the OFDM system which is applied 256QAM and 1024QAM to obtain higher data rate than 64QAM, are evaluated in AWGN and multipath fading environment. Also the system with ADC performance and required SNR are given. This shows 1024QAM OFDM system has capability of an candidate of the higher data rate wireless LAN system, target to 100 Mbps.

Experimental Results of 2.45, 3.5, 5, and 10GHz Radio Propagation Characteristics

This paper reports experimental results regarding radio propagation, transfer, reflection, and scattering characteristics through tempered glass, plasterboard, plywood, plastic tile, and aluminum plate in an anechoic chamber environment at 2.45, 3.5 GHz, 5 GHz, and 10 GHz frequency bands. The time domain measurement method is used for accurate measurement, while the measurement accuracy of the electric wave is 7.5 cm obtained by sweeping 2 GHz bandwidth at the center of the measurement frequency. Simulation results show that fundamental experimental data were obtained for the analysis of actual radio environments, and that the measured data are reliable. The data will be useful for propagation analyses such as ray tracing.

A multipath searcher with the hybrid CDMA interference canceller

In this paper we consider the multipath searcher in a multiuser CDMA system. The conventional configuration where the searcher uses the received signal as its input is studied and a new configuration in which the searcher uses the hybrid interference canceller (HIC) output is proposed. Due to MAI reduction in the the searchers input signal, a much better performance is obtained in the new configuration. For a medium-loaded system, simulation results show that the new configuration increases the detection probability by about 8-40%, and the acquisition-based capacity by 260-360% when the targeted acquisition probability is set to 95%.

Relative Performance of BPSK and QPSK in the Presence of Complex Multiuser CDMA Interference

In a typical mobile communications channel, the multiple accessinterference (MAI) experienced by any user in a multiuser CDMA systemwill be complex-valued due to independent phase offsets betweensignals received from different users. In addition, complex spreadingcodes may also be employed, in which case MAI is complex-valued evenwithout phase offsets. This paper shows that complex MAI substantiallyalters the single-user relationship between BPSK and QPSK modulation,in which QPSK offers twice the bandwidth efficiency of BPSK withoutsacrificing BER versus Eb/N0 performance. Itis shown bothanalytically and through simulations that it is possible to adjustsystem parameters to achieve identical system bandwidth efficiency andBER performance in BPSK and QPSK systems using the conventionaldetector. The performance of the well-known successive interferencecanceller and decorrelating detector are also examined.