Mobile World Congress, the year’s largest gathering of smartphone manufacturers, took place in Barcelona at the end of February and drew a record 85,000 attendees.
New handsets shown at MWC once again demonstrated that as mobile phones evolve into all-in-one devices, combining communications, computing and entertainment functions, they require support for multiple RF standards including Wi-Fi, WiMAX, and audio and video broadcasting. These handsets additionally offer support for Bluetooth, UWB (Ultra Wide Band) and GPS (Global Positioning System) in a frequency range between approximately 800 and 3000MHz. All of these RF standards make mobile-phone designs more complicated, demanding the use of larger numbers of components, resulting in a higher Bill of Materials (BOM) cost, larger printed-circuit-board (PCB) size and increased power consumption.
Traditionally radio communication systems are built with hardware (amplifiers, detectors, filters, mixers, modulators, de-modulators, etc.) dedicated to specific applications that require different frequencies, bandwidths, modulation modes and coding protocols. As a result, from time to time engineers have explored Software Defined Radio (SDR) as an enabler for a flexible wireless architecture, providing adaptability to application demands while offering a degree of future-proofing.
Based on what was seen and heard in and around MWC, SBC once again (it is now 30 years since an engineering team from E-Systems-now Raytheon, coined the term Software Radio) seems to be waiting to take its swings in the on deck circle.
SDRs combine traditional radio hardware with programmability. The key attraction is its ability to support multiple standards on the same processor by only changing the software. This concept has enormous potential benefits for multi-standard wireless applications, such as reduced cost-of-ownership, faster time-to-market and smaller form factor compared with classical solutions.
The idea is to eschew the traditional RF frontend and do as much as you can in software. In an ideal world an SDR receiver would rely heavily on an analog-to-digital converter chip with all the filtering and signal detection taking place in the digital domain. Of course, some RF components like the antenna, LNA (Low Noise Amplifier) and PA (Power Amplifier) still would be necessary in most instances.
As for processor architectures, the SDR could be comprised of general-purpose processors (GPPs), field-programmable gate arrays (FPGAs) or a combination including ASIC/FPGA, DSP/FPGA or massively parallel processors/FPGAs. In several of these scenarios significant amounts of signal processing is handed over to a general-purpose processor. But while the multicore operation of GPPs now allows for increased processing performance, the latest generation of FPGAs is increasingly being used to support processing tasks normally associated with Digital Signal Processors (DSPs) and GPPs.
In any case if you want to design a multi band radio with a single chip you will also run into the necessity of having inductors and filters to limit harmonics, which is not a problem if your SDR is receive only, but transmitters and transceivers need a complicated analog design to meet various regulatory requirements and filtering becomes a necessity.
Let’s now take a look at new and notable SDR developments in and around MWC.
Lime Microsystems, the inventor of the field programmable RF (FPRF) transceiver IC, which can be digitally configured to operate on any mobile communications frequency bands, announced its second-generation device, the LMS7002M. An FPRF is a single chip that is frequency agile, with all the major parameters programmable. The FPRF transmitter takes a digital data stream and converts it into wireless signals, while the receiver performs the inverse operation. Add to this the capability to program key parameters like RF frequency, gain, and bandwidth, and you have the essential ingredients of an FPRF chip. The alternative ways to implement RF designs tend to be a bunch of stand-alone functions such as discrete data convertors and filters, which are normally fixed for a particular specification.
Lime’s second-generation FPRF transceiver extends its low frequency operational range down to 50MHz (previously it was 300MHz). This gives the chip a continuous operational spectrum of 50MHz to 3.8GHz.The chip integrates 2x2 MIMO functionality and supports all cellular standards and frequencies, among numerous other standards such as WiFi. The chip features DSP functions, an 8051 microcontroller, multiple 12-bit ADCs and DACs, LNAs, filters, PLLs and mixers. For more demanding applications, external components can be used to supplement or replace the integrated functions. The on-chip DSP enhances the analog gain and filtering with digital control and is an important factor in reducing overall power consumption. The chip is programmed by a serial bit stream, and designed using a free open source configuration tool suite.
The LMS7002M can operate from a single supply rail of 1.8V with individual blocks capable of being powered down when not required. This makes it suitable for a wide range of battery and mains powered mobile communications devices from small cells and software-defined radios to consumer, machine to machine (M2M) and military radio applications.
At the 2014 MWC Agilent Technologies announced it will participate with China Mobile Communications Research Institute (CMRI) in a joint demonstration of the next-generation radio access network (RAN) as part of the cloud-based radio access network (C-RAN) collaboration project. By way of background, conventional base stations are called RANs, but Cloud-RAN will move the conventional digital base station electronics away from the cell tower and into the data center. The energy savings promises to be significant with only one base station needed to run several radio technologies, instead of individual base stations for each technology.
At MWC, Agilent demonstrated a pure, software-based LTE base station using an IBM server and cloud platform to set up a live connection to a commercial LTE mobile phone, and then made baseband IQ signal measurements using Agilent’s 89600 VSA software.
Analog Devices has announced two SDR platform solutions and ecosystems. This brings its portfolio to four platform solutions that simplify rapid SDR system prototyping and development in applications ranging from defense electronics, RF instrumentation and communications infrastructure to open-source SDR development projects.
The newest addition to Analog Devices’ portfolio of single-channel SDR solutions is the AD-FMCOMMS4-EBZ, a 1 x 1 SDR transceiver FMC module that includes the AD9364 RF Transceiver IC. The AD-FMCOMMS3-EBZ is also a transceiver FMC module and was engineered for 70 MHz to 6 GHz wideband tuning applications such as hand-held and whitespace radios. It is built around the AD9361 RF transceiver on a 2 X 2 SDR rapid prototyping module joining the previously announced AD-FMCOMMS2-EBZ FMC module in the dual channel product portfolio. The new Analog Devices FMC modules include all of the HDL (hardware description language) code and device drivers needed for designers to quickly get their SDR platform up and running on the bench to reduce system development time and risk.
At MWC Altair Semiconductor announced an LTE-Advanced baseband processor it designated as FourGee-3802. Based the company’s SDR architecture, the FourGee-3802 is said to be compliant with the 3GPP LTE Release 10 specifications and software upgradable to Release 11. Combined with the FourGee-6300 companion radio chip, the new baseband processor supports key features including: Category 6 throughputs of up to 300 Mbps, carrier aggregation support for up to 20+ 20MHz channels, a 800MHz CPU subsystem, on-chip HD VoLTE, a wide RF band span of 400-3800MHz with six parallel MIMO RF ports, FastBoost technology for boot and connection time acceleration and ultra-low standby and active power consumption. The part will be mass production-ready in the second quarter of this year.
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Murray Slovick is Editorial Director of Intelligent TechContent, an editorial services company that produces technical articles, white papers and social media posts for clients in the semiconductor/electronic design industry. Trained as an engineer, he has more than 20 years of experience as chief editor of award-winning publications covering various aspects of consumer electronics and semiconductor technology. He previously was Editorial Director at Hearst Business Media where he was responsible for the online and print content of Electronic Products, among other properties in the U.S. and China. He has also served as Executive Editor at CMP’s eeProductCenter and spent a decade as editor-in-chief of the IEEE flagship publication Spectrum.