Power saving is an important issue when integrating the wireless LAN technology into mobile devices. Besides Quality of Service (QoS) guarantee, the IEEE 802.11e introduces an architecture called Scheduled Automatic Power-Save Delivery (S-APSD) aiming at delivering buffered frames to power save stations. In S-APSD, the Access Point (AP) schedules the Service Period (SP) of stations. To increase power efficiency, SPs should be scheduled to minimize the chance of overlapping. In a recent paper, an algorithm named Overlapping Aware S-APSD (OAS-APSD) was proposed to find the wake-up time schedule for a new Traffic Stream (TS) to minimize the chance of SP overlapping. The combination of OAS-APSD and HCF Controlled Channel Access (HCCA) was proved to outperform 802.11 Power Save Mode (PSM) with Enhanced Distributed Channel Access (EDCA) in power saving efficiency and QoS support. However, the OAS-APSD algorithm requires high online computational complexity which could make it infeasible for real systems. Without harming the optimality, this paper presents an efficient algorithm with much less complexity by exploiting the periodicity of service schedule. Because of largely reduced online computational complexity, the proposed algorithm is much more feasible than OAS-APSD.

Power saving is an important issue when integrating the wireless LAN technology into mobile devices. The IEEE 802.11e introduced an architecture named as Scheduled Automatic Power Save Delivery (S-APSD) aiming at delivering buffered traffic to PS stations while meeting QoS requirement. In S-APSD, the access point (AP) of wireless LAN schedules the service periods (SP) of stations periodically. It is clear that the overlapping of SPs should be avoided to increase the power saving performance. An algorithm named Overlapping-Aware S-APSD (OAS-APSD) was proposed to find the service start time (SST) for a new traffic stream to minimize the chance of SP overlapping. However, it takes high on-line computational complexity and thus could be infeasible for real system. Reserving the optimality of finding the suitable SST, this paper presents an efficient scheduling algorithm to utilize the periodic nature of the service schedules. Therefore, with much less complexity, the AP can respond to the joining of new traffic streams in a much feasible fashion when implementing the S-APSD.

The advanced MIMO (multiple-input multiple-output) system can provide higher capacity gain or higher diversity gain in modern wireless networks. The capacity gain is achieved by interference cancellation technique to fully utilize the spatial degree of freedom. In a multiuser wireless system, the increased degrees of freedom provide the chance to select multiple wireless stations (STAs) to maximize the throughput. In this paper, we consider a scenario where the access point (AP) equipped with two antennas to simultaneously communicate with two STAs, each with single antenna. After obtaining the statuses of the size of buffered traffic and the achievable transmission rate, the AP should pair compatible STAs to minimize the loss of spatial degree of freedom. Therefore, three pairing algorithms are proposed and are evaluated through computer simulations. The algorithms have much less implementation complexity than the brute force pairing algorithm and achieve satisfactory performance of throughput.

In the past few years, IEEE 802.11 wireless LANs (WLANs) has rapidly gained large popularity for broadband wireless access. With the growing of various applications, users are demanding features such as higher throughput while keeping respectable operation time for their devices. To provide higher system bandwidth utilization, multi-polling mechanisms are often employed to reduce protocol overhead. However, they require wireless stations (STAs) to spend much time in overhearing which tends to waste energy and reduce battery lifetime. In this paper, we propose an energy-efficient multi-polling mechanism which combines power management strategy with a low overhead Medium Access Control (MAC) protocol. The main idea is to put STAs into the Doze state and determine a suitable wake-up time schedule to statistically achieve desirable guarantee of bandwidth utilization. From both analysis and simulation results, we found that, compared with the original ordered-contention multi-polling scheme, our proposed mechanism saves up to 80% of energy for a network consisting of 20 polled STAs with 5% loss of system bandwidth utilization as tradeoff. The significant saving of energy is a consequence of alleviating the overhearing problem with well scheduled wake-up times for STAs.

Various multi-polling schemes have been proposed to reduce the overhead resides in legacy IEEE 802.11 WLAN protocols. In particular, the two-step multi-polling (TSMP) scheme utilizes the acquired buffer status and channel condition to derive exact required time of each wireless station. Consequently, it seems to be easy to incorporate an energy saving schedule to prolong the operating time of the portable devices. However, even though it adopted the concept of rate adaptation, the TSMP scheme did not take into account frame retransmissions caused by transmission errors due to, say, fading of the wireless channel. The uncertain time spent on retransmission of former stations in the schedule may introduce energy-consuming overhearing for later ones. In this paper, we propose wake-up time schedules and an adaptive updating algorithm to save more energy for the later stations under the error-prone wireless environment. The proposed scheme is simple and thus quite feasible. Besides, from extensive simulation results, we found that the proposed solution is effective.

As the wireless LAN (WLAN) becomes prevalent, users are demanding more and more features such as high throughput and low power consumption. To provide higher channel efficiency, contention-based multipolling mechanism was proposed to improve the single polling and contention-free multipolling mechanisms. However, when this medium access control (MAC) protocol is used, wireless stations would need to spend much time in overhearing which tends to waste energy and reduce battery lifetime. We propose a power efficient multipolling mechanism to arrange wireless stations into groups and put them into sleep mode when other stations are transmitting. From the simulation results, we find the proposed mechanism can address the issue of overhearing while also keeping the flexibility and high channel efficiency properties.

For QoS requirements of real-time traffic, IEEE 802.11 working group introduces a QoS-aware channel access mechanism, called hybrid coordination function (HCF), which consists of contention-based enhanced distributed channel access (EDCA) and contention-free HCF controlled channel access (HCCA). The TXOP allocation and the admission control units of the HCCA reference scheduler are only appropriate for constant bit rate (CBR) flows. It may result in serious packet loss for variable bit rate (VBR) flows. In this paper, we propose a simple admission control algorithm which adopts Gaussian distribution to approximate VBR traffic. Numerical results obtained from computer simulations show that our proposed algorithm can effectively and efficiently allocate transmission opportunity (TXOP) durations to QoS-enhanced stations (QSTAs) to guarantee a predefined packet loss probability. Moreover, our proposed scheme can easily handle multiple VBR flows of the same QSTA to get the advantage of multiplexing gain.