Electronica 2008 - Read our full show coverage from Munich
Recent releases of the 3GPP standard are beginning to include two major technology shifts. First, in release seven, with the HSPA+ addition, which adds a MIMO (multiple input multiple output) radio architecture, and then in release eight, a shift from the high symbol rate serial transmissions schemes used by GSM and W-CDMA, to the slower symbol rate multiple carrier OFDM (orthogonal frequency division multiplexing) technique used by LTE (long term evolution).
For European designers and manufacturers, this is a time to think about what test tools are required to support the next evolution of wireless comms.
The MIMO (Multiple Input Multiple Output) radio contains multiple radios and multiple antennas, which allow multiple data streams to be transmitted at the same time using the same frequency spectrum. These parallel data streams can then be used to either increase data transfer by transmitting different data on each antenna or to increase coverage by sending the same data on all antennas.
Multi-signal transmission and reception increases complexity and poses a number of significant challenges in testing new MIMO-based systems.
One challenge, created by the complexity of MIMO and OFDM, is the increased number of spatial streams that can be supported by the test system. For example, wireless LAN (WLAN), WiMAX, and LTE have provision for four stream configurations. The challenge at the test receiver end is to decompose such a mixed signal into multiple independent signals or streams. But along with this is the challenge involving synchronization.
Successful transmission of multiple signals requires accurate synchronization of multiple channels in phase and sampling alignment. This means that test equipment, such as signal analyzers and generators, must have precise alignment to make accurate and repeatable measurements.
Another test equipment challenge is bandwidth (BW). For instance, WiMAX and LTE currently have a 20MHz BW requirement and WLAN, 802.11n, has a 40MHz BW. This means that test equipment needs to be flexible enough to handle wide bandwidths, ideally without requiring the manufacturer to purchase additional instrumentation.
Mark Elo is director RF product development for Keithley Instruments.
See also: Electronics Weekly's Focus on Wireless, a roundup of content related to wireless communications.