• 전자공학회논문지 IE
• /
• v.43 no.2
• /
• pp.70-74
• /
• 2006

The performance of conventional direct sequence code division multiple access (DS-CDMA) systems is decreased under environments such as additive white Gaussian noise (AWGN), channel distortion and interference noise due to multiple access user. By means of this parameter, auto correlation value of pseudo noise spreading sequence is decreased at receiver. This techniques which are based on correlation of between signature waveform signal. In this paper, to improve correlation property, we proposed the binary chirp DS-CDMA techniques which combine the DS-CDMA and chirp modulation. The proposed system which is based on binary chirp symbol has a good correlation value. Thus, we called BC DS-CDMA. To evaluate the system's performance, we compare the performance of the proposed systems with DS-CDMA systems under AWGN channel and halogen noise which exists on the powerline. The simulation results show that the proposed method has better performance than conventional technique.

• Journal of Communications and Networks
• /
• v.18 no.2
• /
• pp.218-226
• /
• 2016

Coordination among users is an inevitable but time-consuming operation in wireless networks. It severely limit the system performance when the data rate is high. We present FC-MAC, a novel MAC protocol that can complete a contention within one contention slot over a joint frequency-code domain. When a node takes part in the contention, it generates randomly a contention vector (CV), which is a binary sequence of length equal to the number of available orthogonal frequency division multiplexing (OFDM) subcarriers. In FC-MAC, different user is assigned with a distinct signature (i.e., PN sequence). A node sends the signature at specific subcarriers and uses the sequence of the ON/OFF states of all subcarriers to indicate the chosen CV. Meanwhile, every node uses the redundant antennas to detect the CVs of other nodes. The node with the minimum CV becomes the winner. The experimental results show that, the collision probability of FC-MAC is as low as 0.05% when the network has 100 nodes. In comparison with IEEE 802.11, contention time is reduced by 50-80% and the throughput gain is up to 200%.