Wireless Infrastructure Improvements and New Innovations

This chapter brings forward some of the new and emerging wireless communication technologies. It also discusses some of the new wireless technologies that can be expected to materialise in the future due to the demand from the end users, and hence the advances in the research of new technology.

5G

5G (also known as the 5th generation wireless systems, or beyond 4G, or beyond 2020 mobile communications technologies) is one of the upcoming buzzwords for the future’s mobile communication world. It can be seen as a user-centric network, as opposed to the operator centric approach seen in 3G and the service-centric in 4G. 5G is not yet detailed in any particular specification in any official document by any telecommunication standardisation body. However, the 5G terminals are expected be software defined radios that are able to utilise access to different wireless networks simultaneously. They are expected to be capable to download and incorporate new modulation schemes and error-control schemes into use, and they should also be able to join different data-flows together from different technologies (so called multi-mode MTs). The network is going to be the party responsible for handling the user-mobility, while the MT will make the final choice among different wireless network providers for a given service.

Also, greater wireless spectrum allocations, highly directional beamforming antennas at both the MT and BS, longer battery life, lower network outage probability, much higher bit rates in larger portions of the wireless coverage area, lower infrastructure costs, and higher aggregate capacity for many simultaneous users in both licensed and in unlicensed spectrum (Wi-Fi and cellular) are expected from 5G in an article by Li et al. (2009). The article also predicted, that the backbone networks of 5G will move from copper and fibre to millimetre-wave wireless connections.

In the article by Tombaz, Västberg, and Zander (2011) the authors analysed the design limitations for future very-high-capacity wireless access systems, as well as their impact on the overall system architecture. The traditional mobile systems have primarily been limited by the available bandwidth, but for the future, the high-capacity data systems are going to be increasingly constrained by the energy and the infrastructure costs.

Some fundamental assumptions and expectations for future wireless infrastructures can be summarised as:

• It’s not only the energy cost, but also the total access network cost, that are heavily influenced by the number of network BSs. If the energy cost is high, the total cost will be minimised for dense BS deployments.In high-density scenarios, the idle power of the BSs as well as in the backhaul will rise as a significant factor.
• The cost of energy is also strongly reliant on the amount of available spectrum. Significant cost savings in both energy and infrastructure can be made if more spectrums can be brought available.

The optimisation of the MT’s power consumption is vital in current devices, and will also remain as a key factor in the future as well, due to the fact that the battery technologies improve very slowly compared to the evolution of other technologies or MTs that use the Internet to a great degree, improvements in web caching techniques can also bring significant energy savings due to the decreased need to access the network. An alternative solution to relying to BSs for accessing the Internet is to use so called ad-hoc networking, where the WLAN hotspot is reached in multiple hops as opposed to direct access. There are also proposals for concepts where the web content is being shared and cached between those ad-hoc nodes so as to make the web access seem ever more faster.

There are also ways to implement optimised task schedulers for MTs, which aim to meet the deadline for the time limited task in hand by calculating the correct CPU voltage (DVS), and speed for the processor to compute the task, and to make the task’s deadline. Energy is of course also consumed for example in the display, loudspeaker and the device’s CPU, but those were selected to be omitted in this thesis in order to better focus on the network issues.

The potential for very long standby and call times of the MTs today have been made possible by employing schemes like discontinuous transmission (DTX), and discontinuous reception (DRX). DTX in essence just periodically creates time-slots in the transmission protocol, during which the power consuming components in the device can be switched off. DTX is not however feasible (nor supported) in the BSs (in WCDMA/HSPA specifications), as it needs continuous pilot signal transmission. This limitation has already been improved to a certain degree in LTE, due to the fact that the cell specific reference signals are no longer being transmitted continuously – although frequent transmission of synchronisation signals and the broadcast channel still remain.

DRX has similarly the potential for power consumption reduction in the MTs by shutting down most of the MT’s radio circuitry if there aren’t any packets to be transmitted or received. While shut down, the MT only listens to the downlink channel occasionally and may not even keep in sync with the uplink transmissions. In addition, the MT will need to scan the neighbouring eNodeBs to detect any signal quality degradation compared to the serving eNodeB. Should the signal quality of the serving eNodeB prove to be inferior compared to a neighbouring eNodeB, the MT would have to either momentarily exit the DRX mode in order to perform a handover into the superior eNodeB, or perform a cell reselection, after which the DRX may recommence. The MT’s battery savings depend on the DRX parameter settings. On the other hand, as the energy savings gained from DRX build up, so do the packet delays of the MTs engaging in DRX, which can translate to incompatibilities with some time sensitive applications. In the article by Cui, Luo, and Huang (2011) the authors brought up a joint power allocation scheme and proposed an algorithm called Joint Minimisation Power Consumption Algorithm (JMPC-PA). In JMPC-PA multiple transmitters are collaboratively able to select the optimal transmission power with which data can be transmitted over to the users using multiple orthogonal sub-channels. Their optimal power allocation -scheme takes advantage of the good channel conditions in such a way that, upon good channel conditions, more power with a higher data rate is sent over the channel. Should the channel deteriorate again, less power could be sent over the channel.

The basic idea of such cooperative communications is that the nodes in wireless networks can help each other to coordinately transmit the signals, so as to be able to jointly achieve better quality links, or even higher data rates. One typical such technology is called COordinated Multi-Point (CoMP) transmission, which has been considered as an effective tool to improve the coverage of high data rates and the cell-edge throughput of LTE-Advanced. Essentially two coordinated transmission points jointly transmit using their constrained power to the users over multiple orthogonal sub-channels by exchanging the channel state information.