RF front end adapts for increased mobile data demand

The industry is predicting that data volumes could reach 2.7 exabytes per year [1] in 2010 and that volume could increase to between 20 and 90 exabytes in 2015 [2,3],   This expansion is driven by the consumer’s rapid adoption of smartphone and other datacentric terminals, such as datacards, e-readers, and laptops.  In order to support this type of data explosion, operators will need to take a multi-pronged approach: adding spectrum, improving radio link quality, and boost signal quality. To do all of that, they need to rethink the design of the RF front end.

First, they will deploy additional spectrum for data services, which is already occurring with network rollouts in the 700MHz bands in North America, the 2600MHz band in Europe, and 2300MHz band in China. This expansion will require the integration of more bands into mobile devices, which significantly increases the RF component count. Industry experts project that typical handsets will increase from three bands (today) to five bands over the next few years. In the fast-growing smartphone handset segment, the number of supported bands is expected to be even higher -- in the range of 8 to 12 bands [4].

Second, operators will need to improve the radio link quality, which requires lower loss performance from the RF components and an optimized antenna interface.  The antenna is the component most affected by the addition of more frequency bands because it is very difficult to develop an antenna that covers two octaves yet maintains a form factor acceptable for the handset. The reality is, with an increase in frequency coverage, mobile handsets will require tunable antennas which are able to match the performance levels of previous generation phones.

Lastly, operators are reassigning spectrum previously reserved for 2/2.5G technology to next-generation wireless standards such as High-Speed Packet Access (HSPA), Evolved High-Speed Packet Access (HSPA+) and Long Term Evolution (LTE).  These newer technologies are able to support higher data rates and are more spectrally efficient, but they use more complicated modulation schemes which ultimately demands better signal quality from the terminals. In fact, to achieve the target peak data rates of LTE, a signal-to-noise ratio (SNR) of more than 30 dB is needed [5]. This is significant when compared to typical WCDMA systems which require a signal-to-noise ratio (SNR) of only a few dB.

RF front-end limitations
The traditional RF front-end (RFFE) architecture shown in Figure 1 shows all of the signals passing through a single broadband signal path.  This architecture provided adequate performance for low-band-count solutions that were primarily used for voice services.  The challenges associated with this approach for high-band-count data-capable devices are discussed in more detail in the following sections.