The next generation wireless LAN standard IEEE 802.11ax aims to provide improved throughput performance in dense environments. We have proposed an efficient channel sounding mechanism for DL-MU-MIMO that has been adopted as a new sounding protocol in the 802.11ax standard. In this paper, we evaluate the overhead reduction in the 802.11ax sounding protocol compared with the 802.11ac sounding protocol. Sounding is frequently performed to obtain accurate channel information from the associated stations in order to improve overall system throughput. However, there is a trade-off between accurate channel information and the overhead incurred due to frequent sounding. Therefore, the sounding interval is an important factor that determines system throughput in DL-MU-MIMO transmission. We also evaluate the effect of sounding interval on the system throughput performance using both sounding protocols and provide a comparative analysis of the performance improvement.

Handoff is a critical issue for stations in IEEE 802.11-based wireless networks. In order to provide Voice-over IP (VoIP) and real-time streaming applications to stations, a handoff mechanism is needed that can reduce latency and provide seamless communication. However, the IEEE802.11 handoff scheme is not appropriate to supply their quality of service (QoS), because it is based on a full-scanning approach. Full-scanning spends too much time searching for access points (APs). Therefore, various pre-scan handoff protocols such as SyncScan and DeuceScan have been proposed. They scan to find nearby APs before the station loses contact with its current AP, but the pre-scanning overhead is considerable. Our handoff mechanism reduces the delay and overhead associated with the link layer handoff by periodically scanning the channel groups.

This letter derives the packet error rate (PER) in terms of the retry limit and the channel error probability in wireless local area networks (WLANs), when an additional number of retries is allocated to a block of packets to be transmitted. We prove that the lower bound of the PER is the dropping probability which is defined as the probability of any given packet being dropped after its retry limit has been reached.

In this paper, we propose a cross-layer design of packet level cooperation for wireless LANs that support rate adaptation. While keeping compatibility with legacy wireless LANs, distributed control of multi-hop packet transmission is enabled without pre-negotiation of routing or pairing. These features are provided by prioritization scheme based on IEEE 802.11e EDCF in which we set the parameters according to the measured link condition at each terminal. Relaying packets with high transmission rate makes much efficient use of radio resource, and it leads not only to improve performance of the total system, but also to overcome the fairness issue known in rate adaptation, where the terminals with good link conditions cannot gain enough resource because of the time consumed by low data rate transmission. These advantages are confirmed through computer simulations considering packet error rate at each transmission which is assumed by receiving power calculated from the distance between source, relay, and destination terminals. Furthermore, we also discuss about the fairness between cooperation-enabled and legacy terminals when they coexist in the same system, in order to make gradual deployment feasible.

IEEE 802.11 wirelesses LANs (WLANs) have been rapidly deployed in enterprises, public areas, and households. Voice-over-IP (VoIP) and similar applications are now commonly used in mobile devices over wireless networks. Recent works have improved the quality of service (QoS) offering higher data rates to support various kinds of real-time applications. However, besides the need for higher data rates, seamless handoff and load balancing among APs are key issues that must be addressed in order to continue supporting real-time services across wireless LANs and providing fair services to all users. In this paper, we introduce a novel access point (AP) with two transceivers that improves network efficiency by supporting seamless handoff and traffic load balancing in a wireless network. In our proposed scheme, the novel AP uses the second transceiver to scan and find neighboring STAs in the transmission range and then sends the results to neighboring APs, which compare and analyze whether or not the STA should perform a handoff. The initial results from our simulations show that the novel AP module is more effective than the conventional scheme and a related work in terms of providing a handoff process with low latency and sharing traffic load with neighbor APs.

Much research has shown that a carefully designed auto rate medium access control can utilize the underlying physical multi-rate capability to exploit the time-variation of the channel. In this paper, we develop a simple analytical model to elucidate the rule that maximizes the throughput of RTS/CTS based multi-rate wireless local area networks. Based on the discovered rule, we propose two distributed fair auto rate medium access control schemes called FARM and FARM+ from the viewpoint of throughput fairness and time-share fairness, respectively. With the proposed schemes, after receiving a RTS frame, the receiver selectively returns the CTS frame to inform the transmitter the maximum feasible rate probed by the signal-to-noise ratio of the received RTS frame. The key feature of the proposed schemes is that they are capable of maintaining throughput/time-share fairness in asymmetric situation where the distribution of SNR varies with stations. Extensive simulation results show that the proposed schemes outperform the existing throughput/time-share fair auto rate schemes in time-varying channel conditions.

Since Smart Antenna technology has powerful spatial processing ability; it is regarded as a promising approach to enhancing the data rates and capacity of wireless LAN systems. In this paper, a small size, practical switched-beam antenna system, well suited for domestic in-home networking in the 2.4 GHz band, is designed and tested. The system has the configuration of regular nine-prism, and nine 1/4 wavelength rectangular patches are symmetrically distributed on the nine sides of the prism. The switching process is based on control of the microstrip used to feed the patch radiators, by placing PIN diodes at the microstrip feeding lines. The antenna array can generate nine beams with a gain of 11 dB. All the beams generated by the system are cophasal excited and have a 40°beamwidth. Compared to the uniform array, the system can guarantee the consistency of every beam and is preferable in shape.

The IEEE 802.11 distributed coordination function (DCF) provides a contention-based distribution channel access mechanism for stations to share the wireless medium. However, performance of the DCF drops dramatically in terms of throughput, delay and jitter as the number of active stations becomes large. In this paper, we propose a simple and effective scheme, called distributed coordination function with virtual group (DCF/VG), for improving the performance of the IEEE 802.11 DCF mechanism. In this scheme, each station independently decides a virtual group cycle taking into account the current contention level. The virtual group cycle consists of one or more virtual groups and a virtual group includes an idle and a busy period. Each station chooses one virtual group and operates only in the chosen group of the cycle. In other words, each station decreases its backoff counter and tries to transmit its packet during the period of the chosen virtual group like in the IEEE 802.11 DCF. Performance of the proposed scheme is investigated by numerical analysis and simulation. Our results show that the proposed scheme is very effective and has high throughput and low delay and jitter behaviors under a wide range of contention levels.

Supporting quality of service (QoS) capabilities for multi-media applications is one of the major issues in medium access control (MAC) research. In distributed contention-based MAC algorithms, it is a challenging task to support the desired QoS because of the inherent random access characteristics. In this paper, we propose an efficient prioritized fast collision resolution algorithm. The MAC protocol with this new algorithm attempts to provide significantly high throughput performance for data services and support QoS for real-time services. We incorporate the priority algorithm based on service differentiations with the fast collision resolution algorithm, and show that this algorithm can simultaneously achieve high throughput and good QoS support for real-time and data services.

This paper proposes a new scheme that can evaluate the cell throughput performance of wireless local area network (LAN) systems, which use carrier sense multiple access/collision avoidance (CSMA/CA) and multiple transmission bit-rates (multi-rate). We extend the interference model of the conventional scheme in order to deal with interference more accurately in multi-cell environments. Unlike the conventional scheme, the proposed scheme is able to handle multi-rate systems. We use the proposed scheme to evaluate the IEEE 802.11a system and systems whose signal-bandwidth is expanded from that of the IEEE 802.11a system. We find that a system with 35(75) MHz signal-bandwidth achieves about 1.3(1.25) times higher cell throughput than the IEEE 802.11a system. Furthermore, the system with 35(75) MHz signal-bandwidth is also shown to have the potential to achieve up to 1.5(1.8) times higher cell throughput performance than the IEEE 802.11a system if the transmission efficiency on the media access control (MAC) layer is assumed to be ideal. It is concluded that the proposed scheme confirms that the approach to expand the signal bandwidth of the IEEE 802.11a system is effective to improve the cell throughput performance. This result is virtually impossible to derive with the conventional scheme.

In this paper the development of the prototyping platform of a partly reconfigurable System-on-Chip (SoC) for wireless LANs, is described. It is designed to realize both HIPERLAN/2 and IEEE 802.11a wireless LAN systems. The current version of the system includes Mobile Terminal and AP functionality only for indoor use. Future firmware versions (configurations for its reconfigurable part) will upgrade system's functionality to allow its operation in outdoor environments and in wireless point-to-point links. The target System-on-Chip implementation platform will include instruction set processor cores, ASIC blocks and embedded reconfigurable blocks to achieve an optimal balance between implementation efficiency (area, power, performance) and flexibility. The system's prototype is developed on the ARM integrator platform and all firmware versions will be verified before ASIC prototyping.

This paper presents a novel four-sector shaped-beam antenna suitable for base station antennas in 60-GHz wireless local area networks (LANs). The antenna has a plateau configuration, whose four side walls have four linearly arranged microstrip antennas. Each trapezoidal facet excites a shaped beam in the elevation plane in order to meet link-budget requirement between base station and remote terminal, taking account of directional patters of remote terminal antennas. Low-loss curved microstrip-line is applied to connect the three-dimensional antennas with active circuits mounted on a flat carrier plate. This antenna has been adopted as the base station antenna in 60-GHz wireless LANs. The first-stage transmission experiment confirms the usefulness of shaped-beam antennas in the 60-GHz band.