This paper proposes a space division and time division multiple access (SD/TDMA) technique based on intensity
distributions for hybrid line-of-sight (hybrid-LOS) indoor optical wireless communication system. At first, a
novel signal discrimination scheme for the spatially multiplexed optical signals is proposed and it is applied
to a space division multiple access (SDMA) in hybrid-LOS system. In the proposed scheme, multiple terminals
simultaneously transmit their optical signals to access point (AP) using on-off-keying (OOK) modulation, and the
spatially multiplexed optical signals are received by a photodetectors array (PD-array), where multiple PDs are
disposed to observe the spatial intensity distribution of optical signals. Because the terminals transmit their data
using OOK modulation, the spatial intensity distribution observed by the AP equipped with PD-array is subject
to the data transmitted from individual terminals, and the AP can identify the terminals transmitting the optical
signal by determining the transmitted intensity distribution. Of course, the transmitted intensity distributions
are not orthogonal signal and the discriminability of transmitted intensity distributions is much related to the
differences of intensity distributions. This implies that the number of terminals that can simultaneously access to
the AP will be limited and it is determined by the differences of the candidate intensity distributions. In order to
enhance the discriminability of the transmitted intensity distributions, the proposed signal discrimination scheme
is further applied to the SD/TDMA. In the SD/TDMA, the discriminability required to enable SDMA is ensured
by introducing a scheduling algorithm in which terminals with higher discriminatory of transmitted intensity
distributions are allocated to the same time slot. Numerical results show that SD/TDMA using proposed signal
discrimination scheme increases the throughput and the number of terminals that can access to the AP.
KEYWORDS: Signal to noise ratio, Computer simulations, Orthogonal frequency division multiplexing, Relays, Collision avoidance, Information operations, Modulation, Broadband telecommunications, Data modeling, Communication and information technologies
In wireless mesh networks using unlicensed radio frequency band, how to adaptively and efficiently allocate spectrum
among multiple wireless nodes according to the surrounding environment is an important issue. Cognitive
radio that includes functionalities of radio environmental awareness and intelligent radio resource management
in an opportunistic way is regarded as the great candidate to enable the efficient utilization of radio resource.
In order to fully exploit radio resources and enhance spectrum efficiency based on cognitive radio to wireless
mesh networks, this paper proposes dynamic subcarrier selection technique and CSMA/CA (Carrier Sense Multiple
Access with Collision Avoidance) based MAC layer protocol for wireless mesh networks. In the proposed
technique, based on the detection of available spot-wise subcarriers using the subcarrier-level carrier sense and
the estimation of channel conditions, data packet is transmitted using unused discrete subcarriers having good
channel conditions. Numerical results confirm that the proposed dynamic subcarrier selection technique is effective
in utilizing radio resources and enhance spectrum efficiency. Moreover, because multiple nodes can get the
transmission opportunity at the same time, the degradation in transmission performance due to the contention
between multiple nodes can be solved.
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