The definition of Release 10 UE categories builds upon the principles used in Releases 8 and 9, where the number of UE categories is limited to avoid fragmentation of UE implementations and excessive variants in the market. Three new Release 10 UE categories (6, 7 and 8) are specified , as shown in Table, defined in terms of their peak rates which reach about 3 Gbps in the downlink and 1.5 Gbps in the uplink. The highest UE category combines the aggregation of five 20 MHz component carriers with eight MIMO layers in the downlink and four in the uplink. The peak data rate of categories 6 and 7 can be achieved by different means – for example, it is possible to achieve 300 Mbps either by supporting two MIMO layers together with the aggregation of 40 MHz or by four MIMO layers with a single 20 MHz carrier. UE categories supported in Release 10 New Features in UE Category 6,7,8 Approximate supported downlink data rate (Mbps) Approximate supported uplink data rate (Mbps) Number of downlink MIMO layers supported Number of uplink MIMO layers supported Support for 64QAM modulation in downlink Support for 64QAM modulation in uplink Relative memory requirement for downlink HARQ processing (normalized to category 1 level) The Release 8 and 9 UE categories are reused and can in Release 10 support carrier aggregation; for example, a category 3 Release 10 UE may support the aggregation of two component carriers of up to 10 MHz bandwidth each. A category 6, 7 or 8 UE will also signal a category in the range 1–5, to allow backward compatibility in networks which do not yet support Release 10. Additional UE categories are expected to be defined in the future, depending on market requirements.