LTE Trajectory Places High Demands on Baseband Processing

LTE stands for Long Term Evolution, and that is exactly what is happening. At the Linley Mobile & Wearables Conference 2016 we received a preview of what is coming in the mobile and wearable markets. LTE is one of the biggest drivers in this entire domain. There was much discussion about the LTE Release 12 and how it increases bandwidth, boosts efficiency and even offers IoT products an easy to implement low bandwidth and power option, bringing them into the fold.

At the top end of the performance spectrum, LTE Release 12 offers several new Categories for extremely high data rate communication. Look for a whopping 600mbps. The techniques used to achieve this include MIMO, Carrier Aggregation, including aggregation of time and frequency division duplexing, and higher QAM modulation techniques. Things that are coming in Release 13 include dual connectivity so that more than one tower at a time can talk to your handset, adding LAA to take advantage of unlicensed spectrum, and adding WiFi as a peer to offload the cell data link. Additionally, VoLTE is coming and will make all voice communication operate purely as packet data over the LTE data link.

More than ever there is pressure on the baseband system in User Equipment (UE) to work at higher rates and in the most efficient manner possible. With multiple PHY’s there is a struggle to avoid using a dedicated processor for each band. With LTE, 3G, 2G, TD-SCDMA all needing their own radios, it gets pretty chaotic. With dual connectivity and carrier aggregation there will be simultaneous RF streams that constitute the IP data stream for the handset or mobile device.

Baseband processors have become hugely important for optimal UE operation. At the Linley Conference Emmanuel Gresset, Director, Business Development at CEVA, unveiled the newest member of the CEVA-X family, which has an emphasis on PHY control applications. The new CEVA-X2 is the follow on to the previously announced CEVA-X4.

CEVA contends that to handle different tasks in the baseband, a different combination or ratio of DSP versus Control is necessary. The diagram below illustrates this point. Emmanuel emphasized that the CEVA-X architecture combines control plane processing with advanced DSP capabilities. In doing so they are again targeting baseband. While not widely known, CEVA has their design IP in 1 in 3 handsets worldwide.

So what is under the hood? The CEVA-X2 has a 10 stage pipeline, with a 5 way VLIW and 64 bit SIMD. It has 2 scalar units and can perform 4 16×16 MAC and 2 32×32 MAC operations. CEVA has a big differentiation when it comes to its ultra-fast context switching. This is very important when dealing with multiple-RAT. Here is a table with a more detailed breakdown of the X2’s capabilities.

CEVA is suggesting that the reference architecture for the baseband use a single CEVA-X2 to manage the PHY’s. Used this way it can manage the data from the PHY’s without requiring intervention from the DSP. QoS is maintained with flexible priority and task queues. CEVA-X allows for the addition of hardware accelerators. Many of these accelerators are already used in production by tier 1 vendors for 4G and 3G. A partial list of functions includes Viterbi Decoder, WCDMA Despreader, Fast Hadamard Transform, FFT/DFT, MLD MIMO Decoder among others. To compliment the hardware accelerators CEVA also offers communications libraries that are production proven. As you might expect these include LTE-Advanced, LTE, WCDMA, NB-IoT, WiFi-11ac and n, as well as TD-SCDMA.

The applications supported by their reference architectures include wearables with Cat-1, WiFi, GNSS, with voice and audio. The newer LTE specifications include Cat-1 and Cat-0 which are intended for low power and low bandwidth products. In looking at the CEVA reference architecture for LTE UE Cat-12 that supports data rates of 600Mbps, we find the CEVA-X2 in use as well at the very powerful CEVA-XC4500 and the smaller CEVA-X5.

Emmanuel finished his presentation with a view toward LTE Release 13 support and also by looking ahead to 5G, which will roll out in earnest by 2020, but will have selective deployment by 2018. LTE 5G will feature more of everything. There will be much higher data rates, which will come from use of more Carrier Aggregation and more flexible cell architectures – such as micro cells. 5G will be a game changer for machine to machine and vehicle to vehicle communication.

CEVA has a history of design wins in the LTE modem space and seems to be well positioned with its new offerings and its roadmap. for more information on the CEVA-X2 look here. I am looking forward to seeing how the new use models for LTE change not only the scenario of one phone talking to another, but how they change our notions of internet everywhere and connections between machines (M2M) and cars (V2V). The next 5 years will likely show us some of the biggest leaps of vehicle and machine automation ever seen.