Even though the IEEE 802.15.4 standard defines processes for handling the loss of beacon frames in beacon-enabled low-rate wireless personal area networks (LR-WPANs), they are not efficient nor detailed. This letter proposes an enhanced process to improve the throughput performance of LR-WPANs under the losses of beacon frames. The key idea of our proposed enhancement is to make devices that have not received a beacon frame, due to packet loss, to transmit their data in the contention period and even in the inactive period instead of holding pending frames during the whole superframe period. The proposed protocol is evaluated using mathematical analysis as well as simulations, and the throughput improvement of LR-WPANs is proved.

To reduce perforamnce degradations of LR-WPANs due to interference from WLANs, this letter proposes a protocol to allow a piconet to switch an operating channel to an interference-free channel only for transmitting beacon frames. The proposed method does not only increase network performances because of hgh reliability of the beacon frames, but also increase overerall channel utilizations because of using even interfered-channels.

Recently, IEEE 802.15.4 has been standardized for WSNs (Wireless Sensor Networks). This paper proposes an enhanced CCA scheme which involves the data transmission device sending a notifyBusyChannel (nBC) signal in the backoff period when the Channel Using Quotient (CUQ) exceeds 0.5. The CUQ stands for the rate of channel utilization in the previous slot duration. In a single CCA operation, the device nodes are made aware of the busy status of the channel by the nBC signal. We implement the ECCA scheme in a hardware chip for a performance evaluation. The results show that the proposed scheme has short queuing times and less energy consumption than IEEE 802.15.4 CCA. And the scheme is compatible with conventional IEEE 802.15.4 devices.

In the contention access period (CAP) of IEEE 802.15.4 beacon-enabled mode, collision probability increases, and network performance decreases as the number of contending devices increases. In this paper, we propose an enhanced contention access mechanism (ECAM) to reduce the collision probability in low rate -- wireless personal area networks (LR-WPANs). In ECAM, since the duration of each CAP is divided into multiple sub-CAPs, the number of devices contending for frame transmissions in each sub-CAP can be reduced by approximately one over the number of sub-CAPs. Further, this lowers the probability of collision due to two or more simultaneous frame transmissions. In addition, since ECAM shortens the channel access duration of devices, devices with ECAM have lower power consumption. To compare the performance of ECAM with that of the IEEE 802.15.4 standard, we carry out extensive simulations. The results show that ECAM yields better performance than the IEEE 802.15.4 standard, especially for dense networks with a heavy traffic load.

IEEE 802.15.4 is a new standard, uniquely designed for low rate wireless personal area networks (LR-WPANs). It targets ultra-low complexity, cost, and power, for low-data-rate wireless connectivity. However, one of the main problems of this new standard is its insufficient, and inefficient, media access control (MAC) for priority data. This paper introduces an extended contention access period (XCAP) concept for priority packets, also an traffic adaptive contention differentiation utilizing the XCAP (TACDX). The TACDX determines appropriate transmission policy alternatively according to the traffic conditions and type of packet. TACDX achieves not only enhanced transmission for priority packets but it also has a high energy efficiency for the overall network. The proposed TACDX is verified with simulations to measure the performances.

In this paper, we propose a low-complexity frequency offset insensitive detection method for the 2.45 GHz LR-WPAN demodulator. In IEEE 802.15.4 LR-WPAN (Low-Rate Wireless Personal Area Network) specification, the frequency offset as highest 80 ppm in the 2.45 GHz band is recommended for low-complexity, low-cost, and low-power implementation. The proposed detection method is verified such that the performance is within 2 dB of the optimal coherent detection with low complexity, which is less than half in comparison with conventional detection methods.

A direct-sequence ultra-wideband impulse radio (DS-UWB-IR) system is developed for low-power wireless applications such as wireless sensor networks. This system adopts impulse radio characterized by a low duty cycle, and a direct-sequence 0.7-GHz bandwidth, which enables low-power operation and extremely precise positioning. Simulation results reveal that the system achieves a 250-kbps data rate for 30-m-distance wireless communications using realistic specifications. We also conduct an experiment that confirms the feasibility of our system.