Hello Community Members,
Today, In this post I will briefly explain about Channel Bandwidth - LTE Physical Channels.
Introduction to LTE:
LTE (Long Term Evolution) is a vastly deployed technology in cellular networks. It was developed by 3GPP (Third Generation Partnership Project), primarily, to uplift the cellular performance standards of UMTS (Universal Mobile Telecommunication Service). Even though LTE is considered to be Pre-4G technology (or 3.9G), it has extremely high adoption rate by cellular operators across the globe. By 2020, LTE had more than 60% capture of global cellular subscription market. Orthogonal Frequency Division Multiplexing (OFDM) and Single Carrier-Frequency Division Multiple Access (SC-FDMA) are used in LTE technology for downlink and uplink respectively. LTE uses System Architecture Evolution (SAE) network architecture that further consists on Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) & Evolved Packet Core (EPC). EPC carries Home Subscriber Service (HSS), Mobility Management Entity (MME) and Policy Control and Charging Rules Function (PCRF), whereas, E-UTRAN part consists on User equipment (UE) and eNodeB. Depending upon network architecture, LTE usually provides 300Mbps downlink and 75Mbps Uplink speeds.
LTE Channel Bandwidth Overview:
Channel bandwidth is usually referred to effective bandwidth into reuse factor of frequency. It is highest bit transfer rate that a channel can support. Channel bandwidth used by LTE ranges 1.4, 3 10, 15 or even 20MHz. Using Higher order modulation techniques and Multiple Input Multiple Output (MIMO) or Massive MIMO, higher data bit transfer rate can be achieved, Even though, maximum transmission rate, for downlink as well as uplink, remains within the cap as mentioned earlier.
LTE Physical Channels:
There are various forms in LTE network that require flow of data. For this data transfer, three channels are used in LTE – Physical, Logical and Transport. That aligns with the three layers network protocol architecture of LTE.
Physical channels are liable of data & control messages, logical channels act as Medium Access Control (MAC) layer in LTE architecture and Transport channels ensure access of information to MAC and upper layers. LTE physical channel further vary for both streams i-e down and up.
Physical channels are classifiec into downlink & uplink physical channels.
Downlink Physical Channels:
For Downstream, LTE physical Channel has five types: Physical Broadcast Channel (PBCH), Physical Control Format Indicator Channel (PCFICH), Physical Downlink Control Channel (PDCCH), Physical Hybrid ARQ Indicator Channel (PHICH) and Physical Downlink Shared Channel (PDSCH). The first type (PBCH) has 14 information bits, 16 CRC bits and 10 spare bits. It carries the data and information of UEs that require access to the network. The message is repeated every 40ms. The second type, that is PCFICH, is used for intimation of signal format to the UEs. This channel uses 2 blocks coding & QPSK modulation for robust communication. The third type of LTE Physical channels for downlink, that is PDCCH, carries various scheduling information. It uses Downlink Control Information (DCI) message that holds the information about a particular UE. Last but not the least, PHICH channel is for reporting of hybrid ARQs as the channel name suggests. It uses the Acknowledged (ACK) and Not Acknowledged (NACK) signals to indicate the reception or not reception of a transport block. Last but not the least, Physical Downlink Shared Chan nel (PDSCH) is for transmitting user DL data.
Uplink Physical Channels:
For Upstream, the physical channels of LTE are Physical Uplink Control Channel (PUCCH), Physical Uplink Shared Channel (PUSCH) and Physical Random Access Channel (PRACH). PUCCH fulfils different control signaling requirements. It has various formats for different control types. The second downlink channel, PUSCH, acts in the same way as PDCCH does for upstream. Lastly, PRACH is for random access functionality.
Likewise, logical and transport channels have their own types and functionalities that are tailored to for LTE.
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