Networks are all around us. And all networks are different, but what is mobile network? A mobile network is a wireless communications network that is stretched out over a large land area around the world and connected via transceivers at fixed locations known as cell sites or base stations. The old principle of radio transmissions is used by transceivers to connect wirelessly.
The fifth-generation cellular networks are a massive breakthrough in the electrical and electronic industry. Technology has changed the world forever and brought ease and comfort with many added services like autonomous driving, virtual reality, smartwatches, and an ongoing list of devices and gadgets. The addition of such a large number of devices in the same spectrum of radio frequency ranging from 3kHz to 6GHz will increase the burden, latency, and signal interference, if not corrected otherwise. The basic purpose of 5G is to cater increasing data needs as CISCO confirms an increase from 3 exabytes in 2010 to 190 exabytes in 2019 for IP data handling by access networks.
There comes the Fifth Generation communication that involves multiple challenges for scientists and engineers to overcome by increasing the radio spectrum without compromising the range and mobility that 4G and previous generation cellular networks provide. This involves addition of data spectrum beyond previous upper limit of 6GHz ranging up to 300GHz. However, this added band spectrum has its challenges that involve small coverage areas, interference with buildings, obstacles, mountains, and even water droplets or rain.
The solution to all challenges in the way to achieve 5G technology could be solved by adoption, modification, and innovation in five essential areas of technical importance that are millimeter wave, small cells, beam forming, multiple inputs multiple outputs, and full-duplex. Thus the addition of this band spectrum will improve reliability, low latency, improved processing speed, and lesser data interference chances.
What is mobile network?
Joint Allocation of Radio and Optical Resources in cellular networks
An increase in capacity of radio access network (RANs) is possible by introducing additional base stations (BSs) and adding layers of small cells with larger spectral resources and (CoMP) termed as coordinated multipoint for both Transmission and Reception that improves quality and interference protection. Traditional distributed RAN (DRAN) technology does not offer a saleable solution to this issue.
First, because each BS requires a radio unit (RU) and a costly digital unit, the cost of intensifying the network using DRAN would increase linearly with the number of additional BSs deployed (DU). The RU is in charge of transmitting/receiving radio signals and digitizing them, while the DU is in charge of base band processing. Furthermore, the DU needs its own hosting cabinet and infrastructure (e.g., cooling system).
Second, DRAN does not meet the latency requirements of essential CoMP techniques, such as joint transmission (JT), which can coordinate several geographically neighboring BSs to jointly transmit shared data to a UE, therefore increasing throughput by transforming ICI to useful information. JT requires a strict latency constraint on coordination signaling between BSs (1ms or less), but signaling in DRAN takes a long time (4-15 ms). As a result, DRAN does not offer a 5G solution that can compete in market and cater the needs.
In DRAN, increasing system throughput has been thoroughly investigated. It investigates the effect of spectrum allocation in a two-tier DRAN, where small-cell BSs are deployed alongside macrocell BSs. To improve the throughput of mobile back haul service in DRAN, a software-defined optical-access architecture is proposed. Effective signal quantization/compression approaches to maximize CRAN throughput, which is limited by its hefty fronthaul capacity. JT is also gaining traction as a potential approach to boost CRAN’s system throughput.
A virtualized CRAN over TWDM-PON architecture is being considered for combined optimization of heterogeneous resources, such as radio spectrum at radio sites, wavelength bandwidth in fronthaul, and baseband processing resource in DUs. It is called virtualized-CRAN or V-CRAN. As in an independent PON, VPON is a visualized communication route between numerous RUs and a DU over one (or more) wavelength(s).
TWDM-PON can deliver a large number of these VPONs. Over a single wavelength, a VPON can associate geographically neighbouring RUs with the same DU, allowing the DU to access global information about these RUs and coordinate them using specific hardware/software for providing JT services.
A V-BS consists of a set of RUs (comprising the radio resources of the RUs) at cell sites, as well as baseband processing resources in the DU-cloud, a VPON in fronthaul, and a set of RUs (comprising the radio resources of the RUs) in the DU-cloud. A V-BS can be created for each UE so that a group of RUs can send common signals to that UE.
Millimeter Waves in cellular networks
Generally, smartphones use millimeter waves ranging from 3kHz to 6GHz on the radio frequency spectrum. 5G or Fifth Generation technology involves a radio frequency spectrum above 6GHz, reaching 300GHz at the upper limit. The challenges with that wide band spectrum involve the range and strength of signals transmission due to interference and blockage unknown to previous-generation technologies.
The solution to this problem is multiple radio access points introduction and involvement. These transmission systems approach the user device (UE) from various nearby locations. And in case of any interference in the path of one or more sources, it could be easily managed by other sources with the help of transmission-reception points (TRPs) or multi TRPs depending upon the situation and needs. However, there are still chances of interference or coverage failure as visible in the simulation graph below.
Average Rate-of-Reception Failure (%) ∝ UE Speed (km/h). Failure %age Single TRP > Failure %age Multiple TRPs. Additionally, in-mobility mm-wave transmission is possible by adopting intelligent beam search and tracking algorithms for coordinated scheduling and interference management.
It is essential to introduce changes in the design of the antennas transmitting these signals. A patched antenna with microchip inserted having rectangular radiating patch element, ground plane, substrate, and the feeding part is suggested.
Small Cells function in cellular network
Placement of additional transmitters with a moderate number of antennas at common outdoor hotspot locations is a natural solution to increase network capacity. If the frequencies are reused, as previously stated, more cells result in higher capacity. The network variety is raised, and high-speed data coverage is improved. Additional advantages include shorter distances between base stations and terminals and a higher line-of-sight probability.
Small cells will most likely be deployed first at hotspots, resulting in inhomogeneous cell layouts. This necessitates more complicated network planning. Adding tiny cells indoors is also linked to the usage of more powerful enhanced wireless local area networks to overcome the significant outdoor-to-indoor penetration loss, which is often in the 10 to 20 dB range and much higher within large structures. On the other side, there is less requirement for cooperation between indoor and macrocells.
Massive MIMO in cellular network
MIMO in 5g stands for Multiple Input Multiple Output. MIMO is one of the leading candidates for improving wireless communication system capacity, performance, and data rate. MIMO is a technique that uses multiple antennas deployed at the base station and is based on the spatial diversity technique. TDN-PON is a widely used PON method or technique. And Optical Line Terminal (OLT) assigns time slots to Optical Network Unit (ONUs).
WDM-PON is a cheap alternative with added benefits. Changing the PS/C in a TDM-PON with an arrayed waveguide grating (AWG) or WDM multiplexer/demultiplexer (Mux/DeMux) is the difference in the Optical Distribution Network (ODN) between WDM-PON and TDM-PON.
Nine-channel coarse wavelength-division-multiplexed (CWDM) optical channels are used to handle MIMO signals over a single optical fibre. As demonstrated in Figure 5, polarization division multiplexing (PDM) is used in to carry each MIMO stream at a distinct polarization of similar wavelength, utilizing the wavelength’s two polarization.
PDM, employing comb techniques to generate various wavelengths, and a hybrid method between them, are the most widely utilized and demonstrated to be successful. How it uses optical frequency comb techniques and high bandwidth optical modulators (up to 100 GHz) to produce numerous widely spaced wavelengths from a single continuous-wave (CW) laser.
The MIMO technology uses a multipath wireless channel to improve data throughput, range, and interference reduction. As a result, the MIMO system can use multiple MTx transmit antennas on the transmitter side to send multiple parallel wireless signals to multiple MRx receive antennas on the reception side. An MTx MRx MIMO system, such as the 2X2 MIMO system in Figure 6, is frequently used to identify MIMO systems. Multiple antenna approaches are divided into two categories: spatial multiplexing and diversity.
Full Duplex in cellular network
A transceiver using 5G, able to send and receive data on the same frequency at the same time is called full-duplex. Full duplex is a technique that has the potential to increase the capacity of wireless networks at their most fundamental physical layer. The image below shows schematic diagram for highspeed fiber-optic link of the full-duplex coherent communication system.
A 120 Gbps Pseudo Random Bit Sequence (PRBS) generator with a 2 17 – 1 sequence length represents the downlink and uplink input data. The S/P converter splits the incoming bit stream into even and odd bits, which are then sent to the upper and lower 16-QAM modulators, respectively.
The polarization splitter divides the optical carrier into two orthogonal (i.e., X and Y) polarization components, each of which is modulated by a 16-QAM modulator. The internal block diagram of the 16-QAM modulator is what is a cellular network. The QAM sequence generator’s job is to combine four bits into a symbol (which is required for 16-QAM), then feed even and odd position bits to the upper and lower arms, respectively.