1.  Field of the Invention
The present invention relates to a terminal apparatus for a wireless network and a method of adjusting a physical carrier sensing (PCS) threshold in the wireless network, and more particularly, to a method of removing an interference signal or obtaining a spatial division multiple access (SDMA) effect by virtually applying multiple antennae to an orthogonal frequency division multiplexing (OFDM) system and an OFDM based cellular system. 
2.  Description of the Related Art
A wireless mesh network is a communications network made up of a plurality of wireless nodes that are connected to each other using ad-hoc networks, instead of using fixed wired networks, and reciprocally operate.  A network service may be provided in a wide range of areas using the ad-hoc networks, which are constituted by connecting wireless devices based on a net-like structure, as a backbone. 
Using the wireless mesh network, the high installation and management costs required when conventional wired and wireless networks are constructed may be reduced and the networks may have scalability, reliability, and mobility.  In addition, a variety of networks such as ac-hoc networks, cellular networks, and wireless sensor networks may be combined to provide a network in a wide range of areas. 
In spite of these advantages, the wireless mesh network has a lower throughput as compared to that of the conventional wired networks.  That is, since air is a communication medium in a wireless network including the wireless mesh network, the wireless network may be affected by interference caused by peripheral nodes and may not send or receive stable and reliable packets. 
In order to solve such disadvantages of the wireless networks, a system for and method of selecting a data rate in a wireless network is reported in Korean Patent Publication No.  2007-0057089.  Here, a dynamic adjustment scheme is performed so as to quickly adapt to channel variation characteristics, where adjustment values depend on the target packet completion rates that maximize the effective throughput.  In addition, a single effective throughput computation that includes both successful and unsuccessful transmissions is considered to compute the overall message delay.  An objective function considering the waiting time between retransmissions and depending on the MAC protocol is used.  As a result, the performance of wireless systems may be improved using the dynamic adjustment scheme that can quickly adapt to channel variation characteristics by considering the effect of the data rate selection. 
A physical carrier sensing (PCS) mechanism is also introduced according to the IEEE 802.11 MAC/PHY protocol in order to reduce the interference of signals and effectively transmit packets in wireless networks. 
According to the PCS mechanism, a sender node determines whether a channel is in use based on signals (interference and noise generated by peripheral nodes) received by the sender node before transmitting data.  In the PCS mechanism, a PCS threshold provides a reference for determining an idle state.  When the size of a signal received by the sender node is less than a predetermined threshold, the state is determined as an idle state. 
However, the PCS threshold is not standardized by the IEEE 802.11 MAC/PHY protocol.  In particular, a fixed PCS threshold is used in conventional wireless network systems.  But an inappropriate PCS threshold may decrease the performance of a wireless network.  An appropriate PCS threshold is essential to decrease the possibility of packet collisions, maximize the capability of space reuse, and improve the performance of the wireless network. 
The adjustment mechanism for setting an appropriate PCS threshold is classified into a signal to interference and noise ratio (SINR)-based mechanism and a packet loss-based mechanism. 
In the SINR-based mechanism, a sender node needs to receive continuous SINR feedback from a receiver node to obtain a SINR value based on the status of a channel.  This mechanism is difficult to be implemented, and also the appropriate PCS threshold may not be maintained if there is a low packet loss. 
On the other hand, the packet loss-based mechanism, as a sender node-based mechanism, may be designed without the additions of further feedback.  That is, the amount of overhead due to feedback may be reduced.  However, the cause of the packet loss has not been accurately determined.  That is, it is difficult to determine whether the packet loss is caused by interference between nodes or channel congestion.