RFFE System Design Is Key for Network Efficiency and Better User Experience

Updated:2017/9/25 14:43

Author: David McQueen, Research Director at ABI Research and Malik Saadi, Managing Director and Vice President, Strategic Technologies, at ABI Research

 1. LTE to 5G Evolution: Key Device Upgrade Considerations for Increasing Efficiencies in the Network

The network evolution to LTE-Advanced (LTE-A) and LTE-Advanced Pro (LTE-A Pro) are essential enhancements for extending the lifespan of LTE, and critical steps for ensuring a smooth transition to 5G. Not only will these technologies enable operators to launch new high-bandwidth services and unlock new business opportunities, but these upgrades will also dramatically improve network performance in terms of coverage, cell-edge capacity, and spectral efficiency.

Smartphones populating these networks will have a determinant role in augmenting the efficiency of these networks. In order to maximize their effectiveness, it is essential that they are packed with vital RF front end (RFFE) technologies, such as RFFE architectures supporting 4x4 MIMO, envelope tracking (ET), and antenna tuning, while ensuring that all are integrated appropriately into well-constructed modem-to-antenna designs. This article will elaborate on the importance of these components in enabling mobile devices to efficiently tap into these network resources.

2. Defining the Key Parameters for Next-Generation Network Efficiency

The evolution of LTE networks is essential to addressing new business cases and improving speeds, while providing a timely upgrade of networks to address capacity and coverage issues. Technology suppliers must, however, also search for ways to improve network efficiency, a fundamental requirement to serve the voracious data demands of the market and create an improved user experience. This is underpinned by the following key parameters:

•Network coverage


•Spectral efficiency

•Network capacity

The deployment of MIMO—4x4 MIMO and 4x receive diversity (i.e., 2x4 MIMO)—addresses many of these cornerstones, as it helps provide robustness to the radio link by the use of multiple antennas and improves spectral efficiency. It also allows much higher data rates, and better range and reliability.

To enable a better experience for all, a number of particular components in the device are required to help this network transition. Ignoring the modem and effect on battery life, most of these components are related to the RFFE. It is here that each element along the RFFE chain will need some level of upgrade, as these new advanced networks come online. Failure to do so will create inefficiencies and poor user experiences.

The choice of antenna technology, power amplifiers, filters, LNAs, and ET is becoming critical in the LTE landscape, and LTE-A Pro in particular, as devices are expected to handle radio frequencies with different propagation parameters. If the radio platform is not carefully designed to handle this change, it leads to overall transmission degradation and system power inefficiencies.

3. RF Design and Integration of Key Components a Necessity to Take Full Advantage of Network Efficiencies

In an effort to best handle the new features brought about by these LTE upgrades and beyond to 5G, there are a number of RFFE mechanisms required to take full advantage of the network efficiencies achieved through their implementation, namely:


•Antenna tuning

•4x4 MIMO RFFE architecture

ET is crucial as consumers are increasingly sharing content and uplink speeds are improved. Reducing the power consumption of RF power amplifiers (PAs) is a key challenge for smartphone OEMs and is fast becoming the dominant source of handset power consumption. Implementing ET gives up to 30% higher power efficiency compared to average power tracking, and has become a must-have component in smartphones if they are to be used effectively on advanced networks. For the time being, however, ET is the preserve of high-end smartphones, although with the emergence of uplink carrier aggregation (CA) and high-power user equipment (HPUE) that require higher transmit power, there is a growing need for ET to move quickly to the mid- and low-price tiers. ABI Research expects ET to start penetrating the mid-range in significant numbers by mid-2018.

This drive to provide better power efficiency will also witness the arrival of ET-optimized PAs, which allow for tighter integration between the transceiver, ET, and the PA so as to extract more power efficiency from the system in higher bandwidths. Any increase in the power efficiency of a device not only aids battery life, but also directly impacts the effective performance of the network from the user’s standpoint. A device that can transmit a stronger signal at a lower battery current essentially increases the outdoor and indoor coverage area in uplink-limited scenarios, such as being at the cell edge and for indoor VoLTE usage.

Tunable antennas enable significant reduction in the occupied area of a smartphone as they can be reconfigured to cover a wide range of frequencies and dynamically optimize the link to minimize wasted transmit/receive power in real-use conditions. Smartphones are already packed with multiple antennas supporting various modes and bands, so adding extra sets of antennas is challenging in terms of industrial design and RF optimization. In the very constrained environment of smartphones, in terms of both energy and overall form factor, the RFFE system needs to be meticulously designed in order to optimize the overall performance of the device and mitigate interferences, without compromising the integrity of its industrial design and reliability.

Through use of the latest adaptive antenna tuning technologies, the handset can automatically maximize the link quality for transmit or receive. This essentially increases the effective throughput, and outdoor and indoor coverage for links with single or multiple carriers. With a 2 dB to 6 dB improvement in the link, and dynamic signal-to-noise ratio balancing in CA links, the handset extracts more performance from the network. In order for handsets to support an ever-widening frequency range, while maintaining power efficiency, antenna tunability will become key to achieving these ongoing requirements.

Efficient MIMO implementations can improve communications speed in the network by using multiple transceiving antennas, promising significant improvements in signal reliability, higher throughput, better coverage, and increased spectral efficiency without the use of additional transmit power or spectrum resources. As spectral bandwidth is a finite and valuable commodity, MIMO is an increasingly important wireless technique in the drive to make more effective use of available bandwidth. However, with these improvements comes a cost, both in terms of increased smartphone BOM and complexity at the RF level as it remains difficult to squeeze MIMO antennas into LTE devices.

In order to make 4x4 MIMO and 2x4 MIMO (4 receive antennas and 2 at the basestation) commercially viable, RFFE architectures have had to evolve in terms of performance, integration, and cost. RFFE will continue to be a critical sub-system in determining which airlink technologies are practicable in the near future.

As mentioned, HPUE is a technology addition currently being touted to benefit the network through improved coverage as it allows transmit at 3 dB higher compared to standard user equipment (UE), which in relative terms equates to a doubling of output power. Moreover, as throughput in LTE is directly linked to transmit power, an additional benefit of HPUE is higher throughput. Implementation of HPUE requires an upgrade to hardware on the device, necessitating PAs that can handle the generation of more power, while the network only needs a software upgrade. However, HPUE will ultimately have a significant impact on the RF, as all elements along the chain, from the transceivers to PA filters, will have to support double the power, while keeping true to current device size and power constraints.

4. Network Device Population and the Impact of the Technology Mix

By implementing smartphones for use on a network that are built to higher category LTE standards, the user is not only getting a better user experience through higher data rates, but these devices are also more efficient as they use fewer network resources to get these faster speeds. This is where the use of technologies likes 4x4 MIMO and 256 QAM come into their own as more bits can be packed into every LTE transmission, i.e., they enable more bits over the air in a smaller amount of spectrum. For example, high-end gigabit LTE devices have the network sending 4 bps for every 1 Hz of spectrum, whereas lower category LTE devices are getting around 3 bps on spectrum that they are allocated.

This improvement in efficiency owes much to the use of more antennas. On average, a gigabit LTE device uses three antennas to receive data, whereas a lower-order LTE Cat6 smartphone, for example, is capped at using two antennas. This is the influence of 4x4 MIMO, the underpinning technology providing this improvement in network efficiency, but which is not present in Cat6 devices.

Having a higher proportion of users in a network cell with a more efficient LTE smartphone (gigabit) derives the following benefits:

•Throughput speeds improve for those both with and without these types of phone.

•Gigabit LTE devices use fewer network resources to get the speeds needed to service the traffic they are generating.

•An increase in the overall capacity that is of benefit to all smartphone users on the network, irrespective of device type.

As an example, for something like video streaming, both gigabit LTE and LTE Cat6 smartphone users get similar throughput quality, but the gigabit LTE device uses about a third of the spectrum resources for the same quality video. In an age of unlimited data plans, this makes sense to mobile operators who are keen to upgrade to gigabit LTE because higher network efficiencies can deliver more traffic.

In addition, as the speed of throughput on handsets increases, it helps with “bursty” traffic, such as receiving Twitter and Facebook updates, which can be served more quickly by higher order smartphones, freeing up network resources for other users. These higher speeds also mean smartphones are starting to get the same read speeds over the network as flash memory, which helps provide a better user experience when accessing cloud services.

Moving forward, HPUEs are going to be critical as the market advances to 5G NR, most notably at sub-6 GHz, as it can provide up to 30% more uplink coverage in the network. Better battery life is also expected from HPUE devices, although ET will play a crucial role here in reducing power consumption. It would seem that HPUE implementation is inextricably linked to ET, so quick adoption of ET in the mid to low tiers of smartphones will be a fundamental requirement if HPUE is to make a discernible impact.

While the benefits of implementing these technologies into smartphones are clearly needed to induce efficiencies in the network, this is proving difficult for OEMs to achieve as they are incorporated into very few models currently on the market. This is set to change over the next 12 months, as more smartphone models are expected to be launched with these requisite technologies, making them more harmonized with advanced network rollouts, thereby providing marked improvements in efficiencies and user experiences.

However, innovation is not likely to stop there because demand on the RFFE is sure to amplify further as the industry moves to 5G networks, bringing additional complexity through the use of MIMO. Here, massive MIMO, beamforming, and support for additional bands will all become fundamental requirements, resulting in a whole new set of challenges. Moreover, the level of complexity experienced will depend on the spectrum environment as 5G MIMO implementations will hinge on the frequency targeted, either sub-6 GHz or mmWave. Each of these frequencies will need a different MIMO implementation and RFFE design, and our attention will shift to this in upcoming articles, so continue to watch this space.


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