The 5G technology has already arrived in many countries across the world. Whenever a new technology is about to enter, some inter-related terminologies and buzzwords either follow or come to the surface even before the new technology is available. This happened at the start of 4G LTE and is now happening again with 5G. The purpose of this post is to compare the 5G technology with recent developments in the 4G LTE arena so that we can filter out the buzzwords and clarify what 5G is and what it is not. The key LTE technologies that we will be looking at are LTE-Advanced and LTE-Advanced Pro as defined by 3GPP, and another candidate Gigabit LTE which is also in the mix.
Is LTE-Advanced the same as 5G?
The fifth generation of mobile networks, 5G, uses New Radio (NR) technology to provide next-generation mobile services. 5G NR networks can work alongside 4G LTE through a deployment model NSA or Non-standalone. NSA allows mobile operators to launch early 5G services by employing 5G radio base stations together with existing 4G mobile core network, the Evolved Packet Core – EPC. It is an option for those mobile operators who want to utilise their existing 4G LTE infrastructure to launch consumer-centric 5G services like mobile broadband. The other deployment model, standalone 5G or SA, uses 5G radio network alongside a cloud-native 5G core network. This model is the full 5G that enables futuristic use cases around IoT and other machine type services that require ultra-low latency. Check out this post for more information on standalone and non-standalone 5G. The earlier deployments of 5G are likely to be non-standalone, which allows mobile operators to enter the market early without having to invest heavily in an end-to-end 5G network. The non-standalone side of 5G NR is capable of addressing the key consumer-like use cases that we see today. LTE is expected to co-exist and evolve alongside 5G to create an ecosystem that can serve various use cases across different customer segments and industries. LTE is a 4G technology, and even though it can work alongside 5G NR and even in a non-standalone capacity, it is still a 4G technology.
Is LTE still evolving?
The first version of LTE was launched in 2009 and was specified in release number 8 of 3GPP (Third Generation Partnership Project). Since then, there have been various LTE updates in the later releases of 3GPP especially release 10 that specified LTE-Advanced and release 13 that specified LTE-Advanced Pro. Both LTE-Advanced and LTE-Advanced Pro work under the 4G umbrella, and even though release 15 and 16 of 3GPP focused on 5G NR, LTE enhancements have still been part of those releases. Let us now dive into the improvements mentioned above to see what they really mean for the various LTE versions. LTE-Advanced and LTE-Advanced Pro are vital to developing a clear understanding of Gigabit LTE.
In its simplest form, carrier aggregation is a technique that allows a mobile network to combine or “aggregate” multiple frequency channels. This allows a mobile network to assign multiple aggregated channels to an individual user to increase the overall channel bandwidth. As the bandwidth increases, the mobile network can transmit data at a higher data rate to the mobile phone. As per the 3GPP release 8 specification, the original LTE network allows bandwidths to be used flexibly. It enables a mobile network to employ channels of various bandwidths including 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. The value carrier aggregation adds is that it allows multiple channels of these bandwidths to be used together to increase the overall capacity for a single user. LTE-Advanced in 3GPP release 10 makes it possible to aggregate up to 5 carriers (channels). For example, a mobile operator can use 5 channels of 20 MHz each to create a total bandwidth of 20MHz X 5 = 100 MHz.
Improved Modulation technique
While increased bandwidth is achieved in LTE-Advanced and later versions through carrier aggregation, the available bandwidth efficiency is improved by updating the signal transmission technologies. LTE uses two different multiple-access techniques for its air interface. It employs Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) in the uplink. The underlying multiplexing technique is Orthogonal Frequency Division Multiplexing (OFDM) which allows multicarrier modulation. With OFDM, the available carrier bandwidth, e.g. a 20 MHz channel is divided into a large number of smaller carriers known as sub-carriers. These sub-carriers are modulated with the information signal separately using a technique, called QAM (Quadrature Amplitude Modulation). QAM is a highly efficient technique that maximises the number of bits that can be extracted from the available bandwidth through multicarrier modulation. This way, each sub-carrier can efficiently carry data. Since carrier aggregation increases the available carrier bandwidth already, the use of QAM further increases the achievable data rates. Have a look at this post to find out the details of how LTE networks use QAM in OFDM.
Spatial Multiplexing – MIMO
In addition to carrier aggregation and QAM that collectively increase the carrier size and carrier efficiency, respectively; spatial multiplexing ensures that the information signal is transmitted successfully. A spatial multiplexing technique, Multiple Input Multiple Output (MIMO), increases the signal reliability and utilisation of the available bandwidth.
Spatial Multiplexing, in mobile communications, is a technique that allows a mobile network to send a large amount of data to a mobile phone in multiple streams, each carrying smaller chunks of data. For this to happen successfully, both the mobile network and the mobile phone must have the capability to send and receive in this way. This requires technology updates to the base station as well as the mobile phone. Without getting too much into the theory, if you look up ‘Shannon’s capacity theorem’ you will find that the network capacity is a function of bandwidth and the number of antennas. In real life, this means that both carrier aggregation (higher bandwidth) and spatial multiplexing (more antennas) directly impact the overall capacity.
The original LTE, 3GPP release 8 adopted a 2×2 MIMO configuration, which in simple terms means 2 antennas at the transmitter (base station) and 2 at the receiver (mobile phone). LTE-Advanced, release 10, increased this to 8×8 in downlink and 4×4 in the uplink. LTE-Advanced also introduced new categories of devices; category 6, 7 and 8 where UE category 8 supports the maximum number of component carriers and 8×8 MIMO.
License Assisted Access
License Assisted Access is a capability that allows mobile operators to use their normal licensed frequency spectrum in conjunction with unlicensed frequency bands to boost the achievable data rates for end-users. This is potentially a desirable feature for mobile operators because the frequency spectrum is one of the most precious resources of a mobile operator. In competitive markets like the UK, many operators compete for getting hold of larger portions of the licensed spectrum. Unlicensed spectrum can therefore provide a way to fill any potential capacity gaps. This capability was introduced in LTE-Advanced Pro and is also one of the key requirements for 5G NR networks.
So, what exactly is Gigabit LTE then?
The definition and updates for the LTE technology are governed by 3GPP, a partnership of ‘Standards’ organisations, that operates in order to define cellular standards like UMTS, LTE, NR etc. The way it works is that 3GPP have periodic releases and each release contains specifications for new enhancements being introduced in these technologies. The LTE technology was originally introduced in 3GPP release 8 with further updates in release 9. The next major update was the introduction of LTE-Advanced which took place in release 10 and then release 13 that introduced LTE-Advanced Pro. However, 3GPP was not the one that coined the term Gigabit LTE as we can see on their website. Gigabit LTE takes advantage of the key features that were already part of LTE-Advanced and LTE-Advanced Pro specifications. You can check out this post on the difference between LTE-Advanced and LTE-Advanced Pro. According to the sources that were available to 3GPP as per their website, the following is how Gigabit LTE is defined:
- Tri-carrier aggregation
- 256QAM and
- 4×4 MIMO
- Cloud RAN
- Licence Assisted Access technology
Based on the above, the key ingredients of Gigabit LTE are already available in LTE-Advanced Pro. The key technology bits usually mentioned for Gigabit LTE are carrier aggregation, modulation technique, and multiple antennas. LTE-Advanced Pro already allows up to 32 channels for carrier aggregation that easily meets the Gigabit LTE requirement. Also, LTE-Advanced Pro supports the use of unlicensed frequency spectrum which fits well with Gigabit LTE. The higher-order modulation, 256 QAM is in perfect alignment with LTE-Advanced Pro also. Finally, the multiple antenna enhancements through MIMO (Multiple Input Multiple Output) were already available in LTE-Advanced. In conclusion, Gigabit LTE does not require anything that was not already specified by 3GPP in the requirements for LTE-Advanced and LTE-Advanced Pro.
So to summarise:
5G is the fifth generation of mobile networks enabled by a technology called New Radio (NR), and it can work with or without the existing 4G LTE networks. LTE-Advanced, LTE-Advanced Pro and Gigabit LTE are all based on the 4G LTE technology and are not 5G.