Bandwidth Management

To manage bandwidth, one can either attempt to reduce demand or increase capacity. With operators in some countries or markets shifting pricing for data usage from unlimited to tiered, users have become more conscious of how much data they consume. Application (app) developers have also provided tools for managing bandwidth by, for instance, allowing users to specify the maximum size of emails to automatically download. Nevertheless, average usage keeps growing.

Three factors determine wireless network capacity, as shown in Figure 1: the amount of spectrum, the spectral efficiency of the technology, and the size of the cell. Because smaller cells serve fewer people in each cell and because there are more of them, small cells are a major contributor to increased capacity.

Figure 1: Dimensions of Capacity

 Given the relentless growth in usage, mobile operators are combining  multiple approaches to increase capacity, as per the dimensions just discussed:

q  More spectrum. Spectrum correlates directly to capacity, and more spectrum is becoming available globally for mobile broadband. In the U.S. market, the FCC National Broadband Plan seeks to make an additional 500 MHz of spectrum available by 2020. Multiple papers by Rysavy Research and others10 argue the critical need for additional spectrum.

q  Unpaired spectrum. LTE TDD operates in unpaired spectrum. In addition, technologies such as HSPA+ and LTE permit the use of different amounts of spectrum between downlink and uplink. Additional unpaired downlink spectrum can be combined with paired spectrum to increase capacity and user throughputs.

q  Supplemental downlink. With downlink traffic five to ten times greater than uplink traffic, operators often need to expand downlink capacity rather than uplink capacity. Using carrier aggregation, operators can augment downlink capacity by combining separate radio channels.

q  Spectrum sharing. Policy makers are evaluating how spectrum might be shared between government and commercial entities. Although a potentially promising approach for the long term, sharing raises complex issues, as discussed further in the section “Spectrum Developments.”

q  Increased spectral efficiency. Newer technologies are spectrally more efficient, meaning greater aggregate throughput using the same amount of spectrum. Wireless technologies such as LTE, however, are reaching the theoretical limits of spectral efficiency, and future gains will be quite modest, allowing for a possible doubling of LTE efficiency over currently deployed versions. See the section “Spectral Efficiency” for a further discussion.

q  Smart antennas. Through higher-order MIMO and beamforming, smart antennas gain added sophistication in each 3GPP release and are the primary contributor to increased spectral efficiency (bps/Hz).

q  Uplink gains combined with downlink carrier aggregation. Operators can increase network capacity by applying new receive technologies at the base station (for example, large-scale antenna systems) that do not necessarily require standards support. Combined with carrier aggregation on the downlink, these receive technologies produce a high-capacity balanced network, suggesting that regulators should in some cases consider licensing just downlink spectrum.

q Small cells and heterogeneous networks. Selective addition of picocells to macrocells to address localized demand can significantly boost overall capacity, with a linear increase in capacity q  relative to the number of small cells. HetNets, which also can include femtocells, hold the promise of increasing capacity gains by a factor of four and even higher with the introduction of interference cancellation in devices. Distributed antenna systems (DAS), used principally for improved indoor coverage, can also function like small cells and increase capacity. Actual gain will depend on a number of factors, including number and placement of small cells11, user distribution, and any small-cell selection bias that might be applied.

q  Wi-Fi offload. Wi-Fi networks offer another means of offloading heavy traffic. Wi-Fi adds to capacity because it offloads onto unlicensed spectrum. Moreover, since Wi-Fi signals cover only small areas, Wi-Fi achieves both extremely high frequency reuse and high bandwidth per square meter across the coverage area.

q  Higher-level sectorization. For some base stations, despite the more complex configuration involved, six sectors can prove advantageous versus the more traditional three sectors, deployed either in a 6X1 horizontal plane or 3X2 vertical plane

Strategies to manage demand include:

q  Off-peak hours. Operators could offer user incentives or perhaps fewer restrictions on large data transfers during off-peak hours.

q  Quality of service (QoS). Through prioritization, certain traffic, such as non-time- critical downloads, could occur with lower priority, thus not affecting other active users.

Figure 2 demonstrates the gains from using additional spectrum and offload. The bottom (green) curve is downlink throughput for LTE deployed in 20 MHz, with 10 MHz on the downlink and 10 MHz on the uplink, relative to the number of simultaneous users accessing the network. The middle (purple) curve shows how using an additional 20 MHz doubles the throughput for each user, and the top (orange) curve shows a further possible doubling through aggressive data offloading onto Wi-Fi.

Figure 2: Benefits of Additional Spectrum and Offload

Given a goal of increasing capacity by a factor of 1,000, 50X could roughly be achieved through network densification; 10X through more spectrum, including higher frequencies such as mmWave; and 2X by increases in spectral efficiency.