Broadening backhaul capacity through asymmetric transport

Before the iPhone launch in early 2009, AT&T hurried to roll out a major upgrade to its 3G mobile data service for an anticipated tenfold increase in network traffic. The appetite for mobile data and the number of smartphones and data-centric devices have only increased since then.

Data traffic transmitted over cellular networks is expected to grow almost fortyfold until 2015, and U.K. research firm Coda Research Consultancy Ltd. anticipates that mobile video will account for more than 60 percent of all mobile data usage in the United States.

While evolving High Speed Packet Access Plus (HSPA+) and Long Term Evolution (LTE) broadband networks are expected to support this data explosion, operators will also need to resolve network bottlenecks, which are shifting toward the backhaul segment. Fiber-optic deployments, which may seem like the ultimate backhaul solution, require heavy capital-expenditure investment, as well as lengthy deployment schedules.

An alternative and much more economical approach is a unique asymmetric data transmission strategy using microwave networks. This method can increase download capacity by 50 percent, with zero investment in infrastructure or spectrum assets.

Natural asymmetry

Broadband data traffic is asymmetric by nature. Traveling back in time and examining wireline networks reveals a clear imbalance in traffic load.

Wireline networks, originally designed to support telephony services only, provided symmetrical data transmission early on. But with the arrival of the Web and the need to support massive file downloads and video streaming, operators were forced to adapt their networks with an asymmetrical paradigm, implemented through technologies such as asymmetric digital subscriber lines, very high-speed DSL and gigabit passive optical networks.

Today, the ratio of downstream-to-upstream traffic in wireline networks is estimated to be 10:1.

Cellular networks face similar market dynamics and asymmetric traffic patterns. Originally designed to handle voice communication alone, mobile networks now must support massive data downloads as well. This is magnified by the rapid adoption of new devices, such as iPhones, Android smartphones and tablets, and other data-centric terminals.

Figure 1 illustrates the evolution of downstream and upstream ratios in mobile networks. The need for improved quality-of-experience technology to support video and gaming has driven the 3rd Generation Partnership Project (3GPP) to increase the asymmetric pattern of downlink vs. uplink in HSPA+ and LTE networks to ratios of 3:1 to 6:1.

Despite the asymmetric nature of wireless applications, microwave-based backhaul transmission is still symmetrical. The symmetrical configuration holds back precious network resources, including transmission frequencies for unutilized upstream data.

Figure 1. Asymmetric traffic patterns in a 3G network.