## 2 Related Work  
The IEEE 802.11 MAC protocol is widely adopted in various wireless networks. Although the hidden-terminal problem is effectively solved by the virtual carrier sensing mechanism, the exposed-terminal problem still exists, causing reduced utilization of wireless medium. There have been considerable prior work on improving the spatial reuse of IEEE 802.11 MAC. For example, there are schemes focused on analyzing and adjusting the carrier sensing range [7, 8, 9, 20, 21] and control the transmission power [10, 11, 12, 22, 23]. Some researchers tried to modify the behavior of current IEEE 802.11 MAC protocol [13, 24] or the physical layer [14]. Some MAC protocols took advantage of additional hardware devices or advanced physical layer technologies such as an additional transceiver, multiple-input and multiple-output (MIMO), and directional antennas [5, 6, 25, 26]. To improve spatial reuse, [PERSON], [PERSON] and [PERSON] [20] proposed a scheme called Aggressive Virtual Carrier Sensing (AVCS) for activating idle nodes within a reserved range. The basic idea is that any node that receives RTS or CTS packet but not both considers the channel is idle and is free to send. The AVCS scheme may cause additional collisions since the exposed nodes do not consider status and location of their target receiver. Note that the use of directional antennas can also improve spatial reuse, since the area consumed by a transmission is reduced due to the more focused transmissions [5, 6, 26]. However, scheduling of node transmissions become non-trivial since one needs to coordinate the directions of the transmitting antenna and receiving antenna in order to establish a link. Some researchers show that manipulating carrier sensing range can be helpful. [PERSON], _et al._[21] proposed to tune the physical carrier sensing threshold to enlarge the sensing range, such that the entire interference area is covered. With properly tuned physical carrier sensing threshold, all potential interfering nodes will be eliminated, and there is no need for the RTS/CTS handshake. Power control can be used to reduce the interference area such that more concurrent transmissions can be allowed. In [12], [PERSON] and [PERSON] suggested a power control scheme that can eliminate hidden nodes and limit exposed nodes by balancing the carrier sensing range and interference range. The achieved performance improvements, however, are modest as observed in the simulation results presented in this paper. In the MACA-P scheme, a control gap is introduced between the RTS-CTS exchange and the subsequent DATA-ACK exchange, which is used for exposed nodes to transmit their RTS-CTS and for the alignment of the scheduled DATA frame transmission with the current DATA frame transmission [13]. Although some improvements in throughput is achieved in simulations, the additional fixed control gap increases the overall control overhead of IEEE 802.11-like MACs. Such overhead was shown to be as high as 40% in a sensor platform [27], another limiting factor on the IEEE 802.11 MAC performance [4]. In [28], [PERSON], [PERSON], and [PERSON] presented a simple scheme to enable nodes to identify themselves as exposed terminals and opportunistically schedule transmission of a small frame without RTS-CTS exchange. Note that this scheme does not verify the feasibility of scheduled transmissions and the case of multiple scheduled transmissions is not considered, which may cause collision among themselves and high cumulative interference at the current receiver. Simulation results in [28] showed small throughput improvement when the number of nodes is large. The idea of location assisted MAC for concurrent transmissions was exploited in our prior work [15], which considers the two-ray ground propagation model. This work is an extension of the scheme in [15] by considering wireless channel dynamics, i.e., shadowing channels.