5G has been a key topic of discussion over the last few years and a lot has been said about the high-speeds and low latencies. Now that the early versions of 5G networks are already running in many countries, let’s try to understand how the 5G technology works.
5G networks can operate in various frequency bands, starting from below 1GHz and going all the way up to 28 GHz. That allows 5G to achieve latencies below 1-millisecond with higher frequency bands. The lower latency of 5G networks makes them ideal for providing communications for self-driving cars, manufacturing, virtual reality (VR) and other IoT (Internet of Things) services.
What frequencies are used by the 5G technology?
5G networks operate in various frequency bands in order to provide nation-wide network coverage with high data speeds and low latency.
- Low band: Below 1GHz e.g. 700 MHz.
- Mid band: 1 to 6GHz e.g. 3GHz.
- High or Millimetre band: Over 6GHz especially 24-30 GHz.
According to the laws of physics, the wireless signals that have higher frequencies experience higher losses as they travel which means they offer limited coverage. In comparison, the signals that use lower frequencies can travel much further due to experiencing lower losses. Higher frequencies are however more suitable for improved (reduced) latency and higher throughput. Therefore, in 5G, lower frequency bands can be used for providing wide-area nationwide coverage. The higher frequency bands can provide more targetted coverage in smaller areas with low latency and high throughput. Lower frequency bands are also useful for services that require always connected low-powered devices. The lower frequency band for wide-area 5G coverage in Europe is the 700 MHz band. The equivalent in the US is the 600 MHz band.
Is 5G technology FDD or TDD?
In earlier mobile technologies including 4G LTE, 3G UMTS and 2G GSM, Frequency Division Duplex (FDD) has been the primary technique for uplink and downlink. Basically, FDD uses two separate frequency bands; one for the uplink and one for the downlink. 5G uses a slightly different approach. In 5G, the millimetre frequency band can make use of Time Division Duplex (TDD). TDD uses the same frequency band for uplink and downlink and separates the transmission through different timeslots. The lower frequency bands (low and mid) may still use FDD.
Since higher frequency bands (mid and millimetre bands) offer limited coverage, they need to operate in a small-cell architecture for situations that require targetted coverage. Examples of that can include urban areas, office buildings, and manufacturing facilities etc. However, the wider coverage with 5G will require larger cells (macrocells) that can make use of lower frequency to provide better coverage. But that doesn’t mean that macrocells can’t use higher frequencies. Thanks to the beamforming technology that 5G employs, the wireless signal travels to the receiver in a more targetted way with more energy. Since higher frequencies offer higher antenna gains, they also form higher beams which can lead to extended coverage.
5G also enables network slicing which allows mobile operators to offer “virtual” sub-networks. It means they can create individual network slices for specific market verticals (sectors). For example, they can create a very targetted network slice using the millimetre band to achieve ultra-low latency for a manufacturing unit. At the same time, they can create another slice for the rest of the population in the same area for general 5G mobile coverage.
Access technique and channel bandwidth
5G uses OFDM (Orthogonal Frequency Division Multiplexing) which is the same access technology that LTE uses for the air interface. In 4G LTE, the sub-channel spacing is 15 kHz but 5G NR is more flexible and can use sub-carrier spacing in the multiples of 15 kHz e.g. 30 kHz, 60 kHz etc. From a bandwidth perspective, LTE uses a maximum carrier bandwidth of 20 MHz and by using multiple-carriers, it can use up to 5 carriers to achieve a maximum bandwidth of 20 MHz x 5 = 100 MHz.
In 5G NR, the maximum channel bandwidth is 400 MHz and with multiple-carriers, 5G can use up to 16 carriers. That allows the maximum bandwidth to be 400 MHz x 16 = 6400 MHz or 6.4 GHz. Higher bandwidth leads to higher data speeds which allows 5G to offer much higher speeds as compared to LTE.