MIMO and Smart Antennas for Mobile Broadband ... - 4G Americas

SUMMARYIn 2010 this organization, then called 3GAmericas, published the first version of this whitepaper onantennas. At the time, only simulations and very early trials of LTE were available. Since then, alongwith the terrific growth in smart phones and wireless data traffic, the industry has seen importantchanges to the types and methods of deploying wireless systems. Wireless coverage is no longer thedriving force for deployment; capacity is. The need to double capacity each year has resulted in themajor push for LTE, the deployment of 3G Small cells, HET-NETs with WiFi, and residential cellularbase stations. Some operators have deployed 4 branch antenna systems and Remote RadioHeads/Units have become common. Increasingly, operators are integrating more active electronics ontower tops and even inside the antenna radomes. Active antenna arrays capable of verticalsectorization are in trials, and LTE-Advanced standards have been finalized and it has been in labtrials with deployments being planned.In short, the wireless landscape has changed in the past two years and it is time for a refresh of thisdocument.INTRODUCTIONThe extraordinary growth in wireless data traffic is putting immense strain on the operator’s network.To address this demand and increase capacity, operators have five primary tools at their disposal:1) Adding Cell Sites is an effective but expensive approach to adding capacity. In generaladding new real estate is time consuming and increasingly prohibitive. With median intersitedistances dropping from 5km to 2km and recently to less than 200m in dense urbanareas, the operator has less choice in selecting affordable property. Doubling the numberof cell sites approximately doubles the network capacity and the throughput per user(assuming the user density stays constant), and greatly improves the peak user and theaggregate throughput per km2.2) Adding sectors, such as changing from 3 sectors to 6 sectors, is a useful way toapproximate the introduction of new cells. However, this does not quite double thecapacity as the “petals” of 6 sector coverage do not interleave as well as 3 sectorcoverage, and the fractional overlap of 6 sectors is greater. This also challenges handoffprocessing when near highways. This is a common approach in dense urban areas whererooftops are available. There is about a 70% increase in capacity in moving from 3 to 6sectors in an environment with low angle spread (where the base station is located abovethe clutter).3) Adding Carriers (or more accurately, bandwidth) directly adds to capacity. The LTEstandard is particularly adept at utilizing increased bandwidth. In addition, in the USA, theFCC permits increasing radiated power with the bandwidth in the PCS, AWS, and lower700 MHz bands providing improved penetration and coverage. Doubling bandwidth atleast doubles throughput.4) Improved air interface capabilities, such as in evolving from R99 UMTS to Release 5HSDPA, provided well over 4 times the aggregate downlink capacity for example.However, in moving from, say, Release 6 HSPA (1x2) to Release 7 (1x2) with 64QAM and2x2 MIMO we see a more modest ~10-20% improvement in the aggregate throughput.As has been observed before, with improvements in air interface (while leaving everythingelse the same such as bandwidth and antenna configuration) we are seeing diminishingreturns on improvements. It is clear that something more than simply increasingmodulation and coding rates is needed.4G Americas MIMO and Smart Antennas for Mobile Systems – October 2012 – All Rights Reserved4