Hsueh-Wen Tseng

Dynamic backoff for wireless personal networks

Based on IEEE 802.15.4 low-rate wireless personal area networks (LR-WPANs), this paper proposes a memorized backoff scheme (MBS) with the exponential weighted moving average (EWMA) approach to dynamically adjust the size of the contention window. The proposed scheme can be implemented in the standard IEEE 802.15.4 medium access control (MAC) protocol without adding any new message type and without modifying the communicating procedure. An analytic model and a simulation model are developed to evaluate the performance of IEEE 802.15.4, MBS and MBS+EWMA. The numerical results indicate that in terms of goodput, completion rate, average MAC delay, average queuing delay and average number of collisions for each data frame, our proposed scheme significantly outperforms the standard IEEE 802.15.4 backoff scheme.

A Cross-Layer Scheme for Solving Hidden Device Problem in IEEE 802.15.4 Wireless Sensor Networks

The IEEE 802.15.4 standard is designed to achieve low-power transmissions in low-rate and short-distance wireless personal area networks (WPANs). For the sake of reducing the control overheads, the modified CSMA/CA protocol used by 802.15.4 does not have the hidden device protection mechanism, such as RTS/CTS mechanism. Previous studies indicated that the probability of any two devices in an infrastructure network unheard of each other is around 41%. Therefore, the hidden device problem (HDP) results in inefficient data transmission and serious power consumption issues in WPAN. In this paper, we propose a cross-layer detection and allocation (CL-DNA) scheme to solve the HDP in IEEE 802.15.4 without the cost of extra control overhead in data transmissions. The proposed scheme detects relationships of hidden devices based on the overlapped signals and then allocates the hidden devices into distinct subperiods for transmissions. Simulation results validated by mathematical analysis show that the proposed scheme significantly improves the goodput with the reduction in power consumption.

Rotational Listening Strategy for IEEE 802.15.4 Wireless Body Networks

In recent years, interests in the application of wireless body network (WBN) have grown considerably. Wireless body sensor nodes assume deploying a stationary sensor network over a human body area. Among the well-known specifications, IEEE 802.15.4 originally designed for low-power, low-rate, and short-distance wireless personal area networks (WPANs) has become one of the promising candidates for interconnections between wireless sensor nodes. IEEE 802.15.4 uses a modified carrier-sense multiple access with collision avoidance (CSMA/CA) MAC protocol to access channel for transmission data; however, it suffers from inefficient channel utilization because the physical carrier sensing is only performed after the backoff period. In this paper, a rotational listening strategy (RLS) is proposed to increase the rate of successful transmission for WBN. The channel access period is logically partitioned into a number of mini-slots that are individually allocated to nodes. In this case, inefficient channel utilization and collisions can be resolved simultaneously, meanwhile retaining fairness criterion. In addition, an enhanced RLS is proposed to handle the load unbalance situation among nodes. This paper also provides a coexistence solution for the situation where there are nodes without RLS associating with an RLS-enabled WSN. Analytical and numerical simulations are both studied to evaluate the performance of RLS. Both results illustrate that RLS indeed improves transmission efficiency as well as energy consumption.

A fragment-based retransmission scheme with QoS considerations for wireless networks

In order to satisfy QoS requirements for real-time multimedia applications over wireless networks, IEEE 802.11e has been proposed to enhance wireless-access functionalities. However, as system load is heavy, collisions occur most often and then the time needed for successfully transmitting data is lengthened seriously due to contention, handshaking, and long backoff processes for collision avoidance. It is important to keep QoS requirements satisfied. Therefore, we propose a fragment-based retransmission (FBR) scheme with QoS considerations for IEEE 802.11 wireless local area networks (WLAN). By utilizing IEEE 802.11e with FBR, the retransmission delay will be improved to conform strict time requirements for real-time multimedia applications. The capability of the proposed scheme is evaluated by a series of experiments, for which we have encouraging results.

High performance wireless switch protocol for IEEE 802.11 wireless networks

All mobile stations (STAs) in IEEE 802.11 infrastructure wireless local area networks (IWLAN) are coordinated by an access point (AP). Within the 2.4 GHz unlicensed industry, science, and medicine (ISM) band defined in the IEEE 802.11 2.4 GHz physical layer (PHY) specifications, three channels are available for concurrently transferring data packets at the coverage area of an AP. In most of small/medium enterprises or home environments, an AP with one selected channel is sufficient for covering whole service area, but this implies that the radio resources for the remaining two channels are wasted. In order to overcome the drawback, we propose a new and simple media access control (MAC) protocol, named wireless switch protocol (WSP), for increasing the throughput of IEEE 802.11 IWLAN network to support high quality multimedia traffic. This is achieved by allowing any pair of STAs in IWLAN to exchange data packets in one of other idle channels after their handshake with each other in the common channel controlled by AP. Simulation results show that the total network throughput of WSP depends on the time taken by channel switching, and on the ‘Intranet’ and ‘Internet’ traffic distribution, where the Intranet and Internet mean data transmission between STAs in IWLAN and between the STA and wired host, respectively. When all data packets are Intranet traffic and the traffic load is heavy, the ratio of Goodput for the proposed WSP to that of IEEE 802.11 standard approximates 400%. In the worse case of all Internet traffic, the proposed WSP still obtains the similar throughput as that of IEEE 802.11 standard.

A Cross-Layer Judgment Scheme for Solving Retransmission Problem in IEEE 802.15.4-Based Wireless Body Sensor Networks

In IEEE 802.15.4 wireless personal area networks (WPANs), the reliable data transmission is one of important issues such as the body information for medical treatments. Some handshaking mechanisms in literatures were studied and proposed to guarantee successful frame transmission. One of handshaking mechanisms adopts ACK frame, which is replied by the receiver back to the sender when the data frame is correctly received. This is a popular mechanism. However, there are many different reasons causing data frames which cannot be correctly received on the receiver such as the fading channel, data frame collision and hidden terminal problem and so on. Therefore, a sender should have different data retransmission policies and procedures. Neglecting these reasons of failed transmission, the retransmission frame may fail again, and the transmission efficiency will be degraded. In this paper, we propose a cross-layer judgment scheme to solve the retransmission problem. It does not require the cost of extra control overhead, but it can judge correctly the reasons of failed transmission from overlapped signals. Thus, the sender can adjust adaptive system parameters to handle the retransmission procedure. Simulation results demonstrate that the proposed scheme can effectively improve the transmission efficiency.

A safe multiple access-rates transmission (SMART) scheme for IEEE 802.11 wireless networks

The IEEE 802.11 standard and enhanced amendments have defined fourteen transmission rates (1/2/5.5/6/9/11/12/18/22/24/33/36/48/54 Mbit/s) for mobile stations to transmit and receive data frames. With the characteristic of modulation schemes, a higher level modulation scheme requires a higher signal-to-noise ratio (SNR) and, consequently, the data rate is inversely proportional with the transmission distance. Using a higher level modulation scheme, a higher network throughput can be expected; however, the frame error probability will also become higher. Doubtlessly, it is an open issue of selecting a proper modulation scheme for a pair of mobile stations in a time-varying indoor environment. This paper proposes a safe multiple access-rates transmission (SMART) scheme for enhancing the reliability of data transmission in the IEEE 802.11 multi-rate infrastructure wireless networks. The SMART scheme provides reliable transmission by reserving a retransmission period, which immediately follows the transmitted frame and is estimated from a lower transmission rate, for each transmitted frame. If any error occurs on the transmitted frame, the sender will retransmit it right away by using a lower transmission rate to make sure of successful retransmission. Otherwise, the reserved period will be taken by the access point (AP), which often has the longest waiting queue and is the bottleneck in infrastructure wireless networks. The efficiency of the proposed SMART scheme is evaluated by simulation. Simulation results show that the derived performance of the SMART scheme is significantly better than standard under the real environment with asymmetric traffic load.

An Efficient Cross-Layer Reliable Retransmission Scheme for the Human Body Shadowing in IEEE 802.15.6-Based Wireless Body Area Networks

In recent years, a number of middle-aged and elderly people with chronic diseases are increasing. In addition, patients with chronic diseases do not cause health harm in a short period and need long-term hospitalization. Thus, wireless body area network is the best scheme for daily care. According to the human physiological information, it not only sends real-time notifications to users but also reduces delays of the notification regarding patients’ conditions. The physician early identifies the cause of disease and applies remedies according to indications. Daily activities of a person affect the transmission signal of sensor nodes such as walk or run. Thus, the sensor nodes, which have to retransmit the failed frames, are continuously interfered a period time by human body shadowing, so the retransmission procedure should be deferred. If the sensor nodes immediately retransmit the failed frames, they may suffer from the human posture interference again. Therefore, we propose an efficient cross-layer reliable retransmission scheme (CL-RRS) in IEEE 802.15.6 without additional control overheads. The proposed scheme not only detects the information of the sensor nodes with failed transmission frames to allocate retransmission resources, but also increases the successful probability of frame retransmission. Simulation results validated by our mathematical analysis show that the CL-RRS significantly improves frame loss rate and average transmission time, as well as reduces power consumption.

A Cross-Layer Mechanism for Solving Hidden Device Problem in IEEE 802.15.4 Wireless Sensor Networks

IEEE 802.15.4 standard is designed to achieve low-power transmissions in low-rate and short-distance wireless personal area networks (WPANs). For the sake of reducing the control overheads, the modified CSMA/CA protocol used by 802.15.4 does not have the hidden device protection mechanism, such as RTS/CTS mechanism. Previous studies indicate that the probability of any two devices in a infrastructure network unheard of each other is around 41%. Therefore, the hidden device problem (HDP) results in inefficient data transmission and serious power consumption issues in WPAN. In this paper, we propose a cross-layer detection and allocation (CL-DNA) scheme to solve the HDP in IEEE 802.15.4 without the cost of extra control overhead in data transmissions. The proposed scheme detects hidden device relationships based on the overlapped signals and then allocates the hidden devices into distinct sub-periods for transmissions. Simulation results show that the proposed scheme significantly improves the goodput, and with reduction in the MAC delay and the power consumption.

Efficient and fast retransmission for wireless networks

This paper proposes efficient and fast retransmission (EFR) schemes for IEEE 802.11 multi-rate wireless networks. Without major modification of IEEE 802.11 standard, EFR provides immediate data transmission for both ad hoc wireless local area networks (WLAN) and infrastructure WLAN. Also, EFR can compensate for high frame error rates resulting from existing poor rate control algorithms. We develop an analytical model and a simulation model to investigate the performance of EFR. Our study indicates that in terms of average medium access control delay, average queuing delay, completion rate and average collision times per transmission. EFR outperforms standard IEEE 802.11 carrier sense multiple access/collision avoidance mechanism.