Data rates for modern wireless standards are increasing rapidly and this is evident from the trend of cellular standards (shown in Figure 1). The data rate has increased 100X over the last decade and another 10X is projected in the next five years. This trend is partly contributed by using more complex modulations (e.g. using OFDM – Orthogonal Frequency Division Multiplexing - for better spectral efficiency) at the cost of digital signal processing (DSP). In addition, the expansion of channel bandwidth is also an effective way to achieve the data rate increase. This is seen in the wireless connectivity chart (e.g. 802.11) shown in Figure 2. The channel bandwidths for the WLAN standards increase from the traditional 20MHz (802.11g) all the way to 2.16GHz (802.11ad). Because the available spectrum is limited in the low GHz range, for >1GHz channel bandwidth, the carrier frequency is moving from 2.4/5GHz (802.11a/b/g/n/ac) to 60GHz (802.11ad) in the mm-Wave range. With the available spectrum in the 60GHz range, data rates up to 6.76Gb/s can be achieved. Design at mm-Wave frequencies comes with significant challenges, with academic research oriented to the reduction of the power, while industry focuses on product-quality robustness and standards compliance. A new generation of chipsets, compliant with WiGig and 802.11ad, is ready for production.
|Figure 1: Data rate trend of cellular standards|
Since spectrum is scarce, new carrier aggregation techniques are being developed that can combine available channels in a flexible way, e.g. combining non-contiguous channels, or even channels at different frequency bands. The new 802.11af standard aims to utilize “TV white space”, unused legacy analog TV frequency bands below 1GHz. This will first be implemented using a database of available channels per geographical location, but eventually high-sensitivity spectrum sensing will be used to confirm the availability of the spectrum. The possibility of opening up this large amount of spectrum generates radio challenges, e.g. highly linear transceivers that can cover a very wide frequency range and various channel bandwidths. As a consequence of high-linearity and wideband design requirements, distortion cancellation and tunable RF channel-selection techniques are very critical. Most transceivers in this category are adopting digital calibration and analog-feedback techniques to increase the linearity performance for a flexible and tunable front-end to cover a wide range of frequencies.
As wireless technology becomes cheaper, it can be deployed in many devices, including sensors for monitoring environmental conditions. Wireless Sensor Networks (WSNs) require ultra-low-power radio to increase battery life and minimize the battery size, or better yet, eliminate the battery altogether by using energy harvesting. To reduce the power consumption of the radio, the first approach is to use the radio only when it is requested. A “wake-up radio” that monitors the channel and alerts the “main” radio when communication is requested becomes one of the main building blocks of the WSN node. Once the radio is awake, power efficiency becomes the main target for both high- and low-data-rate communication. Another approach is to duty-cycle the radio operation, i.e. only use the radio for short communication bursts, which requires fast turn-on techniques. Such WSNs will enable electronics for sustainability.
Similar to the evolution in cellular, ultra-low-power radios are now becoming multi-standard, covering for example Zigbee, BTLE, and IEEE 802.15.6. Multi-standard implementation implies radio-block sharing, and standards management, including modulation, frequency, bandwidth, power output, sensitivity …, while maintaining the low power consumption, which is one of the key success factors of such devices. Another main concern is the price. These multi-standard radios must have small silicon area circuits in low cost packaging. NFC (Near Field Communication) is becoming more and more popular. This new secure data wireless transmission mode is now embedded in smart phones and will become a de-facto requirement in the next years.
Digital architectures implementing radio functions are very efficient in deep-nm CMOS. In the past years Digital-PLLs were developed in the radio front-ends. Now, new digital approaches are being deployed in transmitters, targeting more flexibility of the RF front-end that leverages CMOS scaling for reduced power dissipation and area, simplifying integration in large SOCs, and empowering the next generation of wireless communications.
|Figure 2: Data rate trend of wireless connectivity standards|
This and other topics will be discussed at length at ISSCC 2013, the foremost global forum for new developments in the integrated-circuit industry. ISSCC, the International Solid-State Circuits Conference, will be held on February 17-21, 2013, at the San Francisco Marriott Marquis Hotel.