# Review of Channel Estimation for Candidate Waveforms of Next Generation Networks
## 2 Structure of Filter Bank Multi-Carrier Systems
### Overview of Next Generation Networks (5G)
#### 2.4.1 PHY/MAC Layer Design Considerations for 5G  
Three broad application categories are used for characterising 5G wireless communication systems. These categories include: enhanced mobile broadband (eMBB), massive machine type communication (mMTC) and ultra-reliable and low latency communications (URLLC). In cellular networks, eMBB is considered for enhancing spectral efficiency of emerging networks as network end users have insatiable demands for mobile data. Machine type communication (MTC), on the other hand, is an advanced model proposed by the 3 rd generation partnership project (3 GPP), where electronic devices and machines are configured to efficiently communicate with one another by the transfer of data over wireless communication networks with little or no human involvements [53; 54; 55; 56]. Transmissionlatency [57; 58; 59] refers to the time interval (delay) that occurs when propagating the input data from the source to the destination over a communication link. In rendering enhanced quality of service (QoS) delivery and user quality of experience (QoE), the emerging 5G networks are specified to offer about 10-100 times higher user data rates and lower energy consumptions in comparison to the present LTE based networks [60; 61]. These networks will also offer ultra-low and reliable end-to-end latency of less than 1 ms [61] with very high reliability (that is, very low packet error rate). The mMTC paradigm of 5G networks will effectively control and manage the collaboration/interaction of numerous network communication devices by ensuring low device complexities for longer device battery life as a result of low energy consumption. For efficient transmission of radio signals between mobile devices and base stations, the PHY and MAC layers of 5G cellular networks are designed to consist of numerous building blocks such as spectrum, multiple access technologies, waveforms, frame structures, coding, modulation, beamforming and duplexing techniques as classified in Figure 7[47]. The waveform candidates for the 5G networks, as shown in Figure 7, include CP-OFDM, UFMC, FBMC, and filtered OFDM (f-OFDM). The classification also include the possible multiple access schemes under considerations for these aforementioned xG networks including: OFDMA, SC-FDMA, resource spread multiple access (RSMA), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) [62; 63; 64; 65]. NOMA is a multiple access scheme that uses power domain for the separation of signals that possess remarkable differences in power levels. The SCMA scheme is a non-orthogonal multiple access technique considered for improving the spectral efficiency and transmission latency of xG networks where input coded data streams (at the transmitter) are mapped to codewords of several multidimensional sparse codewords from specific codebooks. RSMA, on the other hand, is also a potential multiple access technique (under consideration for the upcoming 5G networks and beyond) that uses combinations of low-rate channel and scrambling codes with good correlation properties for the separation of different user signals requiring asynchronous and grantless access. The eMBB service delivery of 5G is designed to offer very high reliability (that is, very low error probability) and high spectral efficiency in digital communication networks. Noise is an unwanted effect that interferes with the transmission of signals as they travel from the transmitter through the communication link to the receiver. The presence of noise in any communication network highly reduces the reliability of the communication system. To guarantee higher reliability of signal transmission and reception over the multipath fading communication channel, accurate error control coding (ECC) is required to enhance precise detection and correction of errors in these communication networks.