As service providers and private network operators seek cost effective solutions to high capacity connectivity, wireless systems are ideal because of their flexibility, speed of deployment, and lower overall life-cycle costs compared to leased-line services. Long distance links require the use of lower licensed frequencies, e.g. 6 or 11 GHz, while short-haul links in the 18 to 38 GHz range can provide highly available services with transmission rates approaching 400 Mbps in a single RF channel. The 80 GHz frequency band offers highly reliable, multi-gigabit transmission at a comparable cost to 18-38 GHz alternatives. This paper discusses the choices when considering licensed band links for short-haul applications, and the performance and cost benefits provided by 80 GHz gigabit wireless systems.
Performance of traditional microwave systems
Conventional fixed wireless systems operating in the 18-38 GHz licensed frequency bands provide data rates from a few T1s/E1s (e.g. 4 – 8 Mbps) up to two OC-3/STM-1 (311 Mbps) and top out at around 400 Mbps for Ethernet transport in a single radio channel. The maximum transmission capacity of any radio system is determined by: 1) the RF channel bandwidth permitted by the regulatory agency, and 2) the type of modulation used. RF channels are typically defined by their carrier frequencies and antenna polarizations. As these systems are usually FDD (Frequency Duplex Division), the RF channel bandwidth is referred to in both the “go” and “return” pairs. For example, a system operating in the 23 GHz frequency band may use up to 56 MHz of RF channel bandwidth (50 MHz in North America) in each direction. In a 56 MHz channel, a simple modulation scheme such as QPSK yields throughput in the 60 Mbps range, while more a complex modulation such as 256QAM could provide almost 400 Mbps.