The Easy Way to a 1 Gbps RF Front-End on Smartphones

One could ask, “Why do we need 1 Gbps download speeds? Aren’t current download speeds fast enough?” Let’s face it: we all hate watching that spinning buffering symbol on our phones, and we always want more data. Carriers want you to have faster downloads too – the faster you get the data, the faster they can shift those valuable spectrum resources to another user. 

In a March 2017 report, Cisco stated that average mobile network connection speeds are currently around 6.8 Mbps – a far cry from 1 Gbps. No wonder we see the buffering symbol spinning on our phone during downloads.

So how can we get to 1 Gbps download and upload speeds on a smartphone? Once you understand the enabling technologies for 1 Gbps and the available RF components, you’ll see that there is an easy incremental path to phones achieving gigabit LTE data rates.
 

The Steps to 1 Gbps: What’s Needed

First, let’s be clear: The road to gigabit LTE is not a jump. Instead it’s a series of small steps in the right direction.

The most direct way to 1 Gbps is to use 3DL CA with 4x4 MIMO on 2 of the 3 component carriers. That’s effectively 10 streams of data in 3 bands. With 256 QAM, that’s 10 x 100 Mbps – which equals 1 Gbps. With a high-performance chipset, 3CA with 4x4 MIMO and 256 QAM functionality can be enabled in the mobile phone, but the RFFE has to be capable.

Below is a simple front-end design using 4 antennas (2 main antennas and 2 diversity/MIMO antennas). This design is a good baseline of what is now available in several smartphones on the market. It’s a simple high/mid/low-band module design that allows for at least 3 CA and covers high-, mid- and low-band LTE frequency ranges. The low-band and midband frequencies are supported by diplexing onto two antennas, while the high band is supported on the other two antennas. The antenna separation/isolation also allows for CA between high band and midband and/or low band.

Incremental Steps to Gigabit LTE Data Rates

With 4 antennas, we have the first requirement for 4x4 MIMO, but those 4 antennas need to be routed to 4 unique radio paths for each spatial stream. Simply put, the configuration where high band had 2 dedicated antennas and midband had 2 dedicated antennas would not support 4 mid/high antennas. It also means we can’t simply rely on antenna isolation to multiplex midband and high-band frequencies, at least not without more antennas.

If we follow the plan of 2 CCs supporting 4x4 MIMO, then we should look to have 8 spatial streams in mid- and high bands. We need to have a way to split out the individual bands on all four antennas – essentially, we need a way to multiplex mid- and high bands. We can assemble an incremental architecture by adding mid/high diplexing on the midband antennas and on the high-band antennas.  

But it’s not always simple to add fixed multiplexers into an existing lineup. A diplexer that splits midband and high-band frequencies is often very lossy, which degrades Rx sensitivity and leads to increased Tx power requirements from power amplifiers. There are implications for current consumption and PA + filter ruggedness to consider as well.

Another option is to include components with multiple mid/high multiplexers (i.e., hexaplexers or septaplexers) to support all the band combinations, but this can be an expensive path forward and quite a deviation from proven designs.
 

Qorvo’s Approach to 1 Gbps: Switched Multiplexers

So, what is the easy step forward on the Qorvo RFFE to achieve 1 Gbps? Flexible mid/high diplexing using switched multiplexers, such as the Qorvo QM17001.

With the QM17001, three configurations can enable a 1 Gbps front-end with little added space and low impact on current proven components. These three configurations are:

1. A low-loss bypass. For low impact when not using 4x4 MIMO
2. Mid/high diplexing path 1. Standard mid/high diplexing that covers most bands
3. Mid/high diplexing path 2. Enabling the difficult cases of multiplexing B30/B40 with midband or high band

 
The radio supports the following modes using the configurations listed above:

• Single band LTE (Configuration 1). The low insertion loss bypass means little impact to current architecture specifications.
• DL CA (Configuration 1). Mid/high diplexing without MIMO can still be supported with antenna isolation.
• 4x4 MIMO, single band (Configuration 1, 2 or 3). For high band, QM17001 can be enabled on the midband paths, creating a route for additional receivers. A similar configuration is possible for midband using the QM17001 on the high-band paths. The primary Tx path is still in bypass mode, so the impact is low.
• 4x4 MIMO, mid/high diplexed (1 Gbps) (Configuration 2 or 3). All QM17001’s are enabled and the mid/high diplexers introduce loss.

 
In summary, you can achieve a 1 Gbps LTE RFFE with incremental changes to existing architectures, and Qorvo is here to help you make that happen. For more information, visit Qorvo’s RF Fusion™ web page. For technical guidance and applications support, please visit our Technical Support web page.