Multimode: How to design a programmable baseband device for multiple wireless standards

From consumers who demand to be connected wherever they are and using the fastest connection speeds possible, to the developers of products for the multiple emerging 4G standards that will feed this demand, the level of choice available to all parts of the entire chain makes it difficult to evaluate the perfect choice for product design and which wireless standard to implement.

Different transceiver standards and protocols are diverging, though all drive towards 4G with space-time diversity, space division multiplexing, beamforming, CDMA, and OFDMA. HSPA, LTE, WiMAX, and IMT-advanced will therefore be co-existing, as will 802.11g/b/n.

At the same time, different countries have set up barriers by using different digital broadcasting standards—DVB-T/H, ISDB-T, DMB-T, T-DMB and DAB are fighting for their place as the ultimate protocol. As a result, it is inevitable that there will be multiple implementations depending on the scenario for which the product is being developed (see Figure 1).

Click here for Figure 1.
Figure 1: The convergence of all the different standards will result in them being required in many different applications as seen in the center of this diagram.

This kind of mobility and convergence requires the ability to switch and process different protocols to keep connected with multimedia services through the different environments that a user may be crossing during the day—in other words, multimode support.

Multimode requirements
So the baseband processor needs to be able to support several different modes, and be capable of switching between them. At the semiconductor device level, this means the manufacturer needs to be able to implement a programmable solution, ideally integrated into the main application processor creating a new breed of value added devices way beyond the current view of communication devices.

Typical programmable baseband processing solutions have addressed the challenge of addressing multiple standard modem requirements by simply extending the ability to better handle the extra data processing required.

The main disadvantage this poses is that the design is only making an attempt to handle the extra volume of data processing without looking at how the extra data flows through the system—or worse, how you can actually program it.

But as baseband processing gets more and more complicated with each generation of standard, and with the need to support more and more standards using one device, it doesn't become a viable option to simply design the device to handle larger data processing. All this does is to increase the power consumption requirements, and this impacts battery life.

By focusing on improving the processing of data, the traditional programmable baseband processing solutions neglect the very significant effects of moving data around and of the ability to program the solution.

Such systems end up being far more complicated than is needed because the real bottlenecks are not being addressed. Ultimately this reduces battery life which doesn't seem sensible if the product is meant for mobility (although anybody who has a 3G phone knows that is the reality today); 4G standards are even more complicated so if nothing changes things are only going to get worse.