Coexistence of Heterogeneous Networks over White Spaces

Several nations have approved the unlicensed use of TV white spaces (TVWS), under the condition that secondary (unlicensed) users do not interfere with incumbent primary (licensed) users. As a result parallel efforts are on in several different standardization groups (for IEEE 802.11, IEEE 802.16, IEEE 802.22, Weightless etc.) to develop wireless standards for secondary TVWS usage. A key challenge which we address in this paper is the coexistence of different secondary wireless technologies in TVWS. While some technologies such as WiFi (IEEE 802.11) are designed for unlicensed usage, others such as WiMAX (IEEE 802.16) are designed assuming exclusive use of spectrum. WiFi communications coexisting in the same TVWS with WiMAX (or WRAN (IEEE 802.22» will potentially disrupt the latter's ability to provide QoS in terms of latency or bandwidth guarantees. In this paper we present a minimal overlay Medium Access Control (MAC) protocol that can serve as a wrapper over heterogeneous MAC layers and allow them to coexist while reducing mutual interference. We show that our MAC layer wrapper is spectrum aware in the sense that it promotes the use of disjoint TV channels by different wireless networks if several unused channels are available; is coexistence aware in the sense that it enables non-disruptive communication if more than one network occupies the same TV channel; is QoS aware in the sense that it can distinguish between networks with varied QoS requirements and promotes channel sharing likewise. In this paper we describe our overlay MAC layer design and present evaluation results obtained from simulating our MAC protocol. We give experiments to support our choice of design parameters. We analyze trends for our protocol based on a new metric "Error in Distribution" and show the feasibility of prioritized Coexistence.