A survey of MAC issues for TV white space access

Keywords: TV white space Cognitive radio Medium access control Survey Open research issues a b s t r a c t The opening of TV white space (TVWS) bands for cognitive access is one of the first tangible steps to solve spectrum scarcity problem in current wireless networks. However, this has also raised many new challenges to efficiently use the TVWS spectrum. One of the primary challenges is the design of efficient Medium Access Control (MAC) protocols that conform to various rules imposed to protect primary users as well as accommodate spatio-temporal variations of the TVWS spectrum. This article presents MAC-related challenges related to cognitive access to TVWS, discusses potential approaches to overcoming these challenges, and investigates open research issues. It also reviews regulatory activities in several countries and worldwide standardization efforts for TVWS access. The spectrum scarcity problem is becoming more and more challenging in current wireless networks due to exponential growth of wireless traffic. The Cognitive Radio (CR) paradigm has emerged as an efficient method to improve spectrum usage and help to address the spectrum scarcity problem. The idea of CR is to allow unlicensed devices to access underutilized licensed spectrum without causing harmful interference to incumbent communication services. The U.S. Federal Communications Commission (FCC) has published its final regulations to allow unlicensed radio devices to operate in the broadcast television spectrum at locations where that spectrum is not being used by licensed services. The spectrum is termed ''TV white space'' (or ''TVWS''). TVWS access is a promising method to address spectrum scarcity problem due to large amount of TVWS spectrum resources and better propagation properties of TVWS channels. One of the primary challenges of TVWS access is the design of efficient Medium Access Control (MAC) protocols. The cognitive MAC protocol is required to not only protect primary users (PUs) (e.g., TV stations and wireless microphones) from harmful interference caused by secondary users (SUs), but also deal with spatial–temporal variations of TVWS. Additionally, a cognitive MAC protocol must enable the coexistence of heterogeneous TV band devices (TVBDs) to operate in TVWS, which is very challenging due to significant differences of these TVBDs in terms of signal characteristics (such as bandwidth, modulation and power spectral density), transmit power levels, PHY/ MAC techniques and mobility characteristics. Furthermore, increased mutual interference in TVWS makes the design of cognitive MAC protocols more difficult. More specifically , mutual interference in TV bands is …