Ready, Set - is 5G ready for mmWave?
The race is on to be first to 5G. AT&T and Verizon have announced that they will have first commercialization of 5G mmWave products and networks this year. Verizon announced a pre-standard service on Oct 1st and plan a 5G NR compliant service in 2019. mmWave frequency bands offer wider channel bandwidths, which enable the higher data throughputs expected in 5G. While the use of mmWave frequencies is not new for communications, it is new for cellular and comes with many new design and implementation challenges.
mmWave operating bands will support the enhanced mobile broadband (eMBB) use case for high data throughput applications like streaming UHD videos and movies. There have been numerous demonstrations and trials at mmWave frequencies.
- At the PyeongChang Winter Olympics in South Korea, Samsung, Intel, and Korea Telecom collaborated to showcase mmWave 4K streaming service at 28 GHz using a 5G network.
- In Japan, NTT DoCoMo is working with Huawei and NEC on field trials to demonstrate mobile communications at 28 GHz.
- AT&T and Verizon have been conducting mmWave trials in select US cities. According to the HIS 2017 Markit report, the first commercial mmWave introductions are expected to be fixed wireless access (FWA) in the US.
New challenges implementing radios at mmWave frequencies must be addressed in order to create a quality user experience.
At mmWave frequencies there’s increased path loss, blockage, and other propagation issues that will limit performance and coverage. To overcome these signal propagation issues, multiple antenna elements will be combined to create narrow beams with higher antenna gain. These narrow beams will be configured as beam steering or beamforming so that the signal can be directed to specific users. With the use of these narrow beams, the base station and the device need to know each other’s location in order for the beam to be properly directed, making it difficult to establish and maintain a quality communications link, especially if the device is mobile.
5G NR Release-15 provides new initial access procedures and beam management functions to ensure a device can connect and travel through the network. The base station uses beam sweeping to transmit basic system information and synchronization signals in sync blocks across the spectrum, and the UE determines the strongest match and transmits back to the base station. Now the base station knows the direction on which to transmit to the UE an the UE knows the direction for which to receive from the base station, and a communication link can be established. Procedures are defined for beam acquisition and tracking, beam refinement, beam feedback, and beam switching.
Beam patterns must also be in the correct formation and location to achieve the maximum radiated efficiency of the signal. Antenna gain, side lobes, and null depth need to be validated through over-the-air test methods for the range and bandwidth of the antenna.
Improvements in data rates will also come from the use of wider channel bandwidths in frequency range 1 (FR1: 450 MHz to 6 GHz). Many countries are freeing up spectrum in the 3.4 to 3.9 GHz and 4.4 to 4.9 GHz frequency bands where more contiguous spectrum is available. Up to 100 MHz channel bandwidths can be aggregated to a maximum of 400 MHz in FR1. Also, techniques like LAA (license assisted access) will be supported in 5G NR Release-16 to achieve higher data rates by aggregating a secondary data channel in unlicensed frequency bands.
Implementations in sub-6 GHz will be more of an evolution from previous cellular communications, but not without its own challenges. Challenges achieving good signal quality in the wider channel bandwidth and coexistence with adjacent and shared spectrum will need to be evaluated.
Ready, Set - Is 5G ready for mmWave?
There have been many demonstrations of 5G in action both in fixed wireless and mobile scenarios. We are seeing the first commercial releases with mmWave access, but the real question for me is about performance and reliability when a device is mobile.
mmWave frequencies have issues with path loss and signal propagation. Until more research and validation is done to ensure reliable mobile scenarios, capabilities will be very limited. Initial releases will focus on fixed wireless access (FWA) and will rely heavily on FR1 operating bands as back up. There’s still a way to go before we’ll see mass commercialization of 5G mmWave specific devices for mobile communications.
Find out more about the challenges developing and testing 5G devices in mmWave spectrum in the following white paper series: First Steps in 5G: Overcoming New Radio Device Challenges Series.