© IMAGESTATE IEEE SIGNAL PROCESSING MAGAZINE [50] SEPTEMBER 2006 1053-5888/06/$20.00©2006IEEE [ Roland Kempter, Peiman Amini, Christian Schlegel, and Behrouz Farhang-Boroujeny ] On Coverage and Routing in Wireless Ad Hoc Networks [ IEEE 802.11 versus CDMA technology ] R esearch in ad hoc networks faces a multitude of challenges from the physical up to the transport and network layers. Because of the scarce wireless resource and tight capacity limitations [1], a num- ber of cross-layer designs have been proposed recently [2], [3] that deal with optimizing all aspects of data communications in the ad hoc scenario, especially routing and TCP (transmission control protocol) over ad hoc networks. However, fundamentally, networking performance such as delay, throughput, and connectivity are determined by the physical layer; unfortunately, the majority of these designs are based on the IEEE 802.11 protocol, which is known to lead to congestion, connectivity loss and increasing delay as the load builds up. STATEMENT OF THE PROBLEM: IEEE 802.11 VERSUS CDMA TECHNOLOGY IN AD HOC NETWORKS Ad hoc networks typically use IEEE 802.11 or similar protocols, mostly due to availability and ease of deployment, along with spe- cialized routing protocols such as ad hoc on demand distance vector routing (AODV) [4] and the dynamic source routing (DSR) protocol for mobile ad hoc networks [5]. Yet IEEE 802.11, in addition to possible throughput degradation as the number of transmissions increases [6], faces issues such as the exposed and hidden node problem, which is especially problematic in multi- hop ad hoc networks. As a solution, the IEEE 802.11 distributed coordination function (DCF) with its four-way handshake of Request-to-Send/Clear-to-Send/DATA/ACK (sometimes simply referred to as RTS/CTS) has been added to the standard. RTS/CTS is used to signal the nodes in the network that a trans- mitter requires access to the channel; in other words, the RTS/CTS message exchange represents a resource reservation process. Nonetheless, in the ad hoc scenario this very mecha- nism has been shown not only to be ineffective [7] but may actu- ally cause additional congestion [8]. While it is well known that the RTS/CTS scheme is not efficient, it may in fact cause colli- sion rates as high as 60% at higher loads [9]. Furthermore, because of such high collision probability, back-off times and thus required buffer sizes increase. As a possible solution, delay busy tone multiple access (DBTMA) has been proposed to ease the collision problem. In this method, two narrow-band frequen-