4G Americas Carrier Aggregation_FINALv1 0 (2)

In an effort to be efficient and to reduce handset size and weight, manufacturers of handsets (andchipsets) reuse various internal hardware components across many similar mobile bands. Antennas,diplexers, linear amplifiers and other RF devices are shared between bands. In order to support the CAof two low band frequencies, it may be necessary to build devices that require additional RF hardware toseparate the two radio signal paths. This additional hardware may result in devices with increased weight,size, complexity and cost.The low band and high band case discussed in the previous section does not have this limitation as thehandheld device’s RF components are probably already separate for the two bands.In addition, the handset and chipset vendors, as well as the manufacturers of base station equipment,must consider tight filtering and other interference mitigation techniques in their designs. These featuresreduce cross-modulation and intermodulation, which could occur with multiple transmitters/receiversbeing operated simultaneously in close proximity. These are examples of why operators should consultwith their RAN infrastructure vendors, as well as their device and chipset manufacturers, whendeveloping their CA implementation plans.6.2.3. HIGH AND HIGHER BAND CAIn a similar case to the low and lower band example described above, some operators will want to useCA techniques to provide their subscribers with an enhanced bandwidth experience using their multiplehigh band spectrum holdings. For instance, an operator may want to aggregate its AWS and 2500 MHzspectrum.The technical challenges here are similar to the low and lower band scenario. Reuse of RF componentsin the manufacture of the handheld device must be considered. Also, filtering in the handset and in thebase station must be well designed to minimize interference between carriers and components. So onceagain, operators should consult with their RF infrastructure and their device vendors when developingtheir CA strategy.CA_2A-4A is an example of a high and higher band CA case that aggregates two DL component carriersfrom Band 2 (PCS 1.9GHz) and Band 4 (AWS 1.7/2.1GHz) to provide 40 MHz (300 Mbps) of aggregatedbandwidth. The combination also defines bandwidth combination set 1 that allows an aggregatedbandwidth of 20 MHz (150 Mbps). As both bands are consistent in coverage, this combination is primarilyfor higher capacity and throughput vs coverage. In this specific use case aggregation of two high bandsrequires a quadplexer in the device as defined in Section 7.3.6.3 FDD-TDD CA [5]Previously, CA has been possible only between FDD and FDD spectrum or between TDD and TDDspectrum. 3GPP has finalized the work on TDD-FDD CA, which offers the possibility to aggregate FDDand TDD carriers jointly. The main target with introducing the support for TDD-FDD CA is to allow thenetwork to boost the user throughput by aggregating both TDD and FDD toward the same UE. This willallow the network to boost the UE throughput independently from where the UE is in the cell (at least forDL CA).TDD and FDD CA would also allow dividing the load more quickly between the TDD and FDDfrequencies. In short, TDD-FDD CA extends CA to be applicable also in cases where an operator hasspectrum allocation in both TDD and FDD bands. The typical benefits of CA – more flexible and efficient4G Americas LTE Carrier Aggregation October 2014 32