Despite difficult financial conditions, global mobile phone usage continues to grow. More than 3.9 billion subscribers currently use 3GPP-based technology networks.1 As a result, major network operators around the world (and not just 3GPP operators) are pressing ahead with their plans to roll out the next generation of cellular technology—Long-Term Evolution/System Architecture Evolution (LTE/SAE).

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Although high peak data rates grab headlines, the objectives of LTE/SAE are as much about increasing efficiency and reducing costs as achieving high performance. Great efforts are being put into creating a global standard to achieve global economies of scale. Despite this, the 3GPP Rel-8 LTE/SAE networks will see regional variations in deployment. Different frequency bands will be used in different parts of the world. Different LTE modes (FDD and TDD) also will be used. And, different legacy networks will be used for fall-back—GSM/GPRS/WCDMA/cdma2000.

As with any major change in technology, the adequate testing of LTE devices needs to be considered. With this requirement to support multiple radio access technologies in multiple frequency bands, the complexity of devices continues to rise, while consumers expect smaller devices (at least, no larger than the previous generation) with higher performance and lower power consumption. Providing network operators with stylish, high-performance devices at competitive prices to keep customers coming back for upgrades has never been harder.

Why Is It A Challenge?

High performance, wide bandwidths, high data rates, fast response times (reducing latency), more complex antenna configurations—and that’s just the LTE part—all combine to present greater challenges to the development of next-generation devices. To support roaming onto other network technologies, multiple radio standards will need to be supported, especially with the lack of voice support in early LTE networks.

For much of the world, LTE devices will need to be backed up with GSM/GPRS, WCDMA/HSPA, and/or cdma2000/1xEVDO support in a range of frequency bands, with downlink frequencies potentially ranging from 746 MHz to 2.69 GHz.2 Initial certification of LTE devices is expected to be in Bands 1 (2.1 GHz), 7 (2.6 GHz), and 13 (700 MHz) for FDD mode and Bands 38 (2.6 GHz) and 40 (2.4 GHz) for TDD mode. The WRC-07 conference allocated further spectrum for mobile use, meaning both lower (down to 450 MHz) and higher frequencies (up to 3.6 GHz) are likely to be seen as LTE rolls out over the next five years.

In addition, major network operators are emphasizing support for both FDD mode and TDD mode for two reasons. First, LTE TDD mode is the accepted upgrade path for Chinese 3G networks and is being championed by China Mobile, one of the major network operators. Second, many network operators in other regions have unused spectrum that is allocated for non-paired operation, so this could be used for LTE deployment. Spectrum (or lack of it) is one of the major issues facing LTE operators, with the need for up to 20-MHz blocks to achieve the 100-Mbit/s headline data rate.

Another challenge for LTE devices is maintaining data throughput rates at cell edges, where the signal-to-noise ratio (SNR) is usually worst, and also in crowded cell conditions. For these situations, optimized receiver performance is essential, making the best use of the available signal in a noisy environment.

The typical form factors for LTE devices are likely to be USB sticks, dongles, and PC cards in addition to the internal chipsets that will be integrated into laptops and high-end PDAs and smart phones. Thermal management will be important in these compact devices when so much functionality needs to be incorporated.

It will be difficult for any single design to meet all of the possible requirements: achieving the highest data throughput and lowest latency with the lowest power consumption and covering most frequency bands while remaining as compact as possible. These are the challenges facing designers.