In the field of wireless communications, each technology employs a unique set of physical layer channels to facilitate efficient data transmission and network management. These channels, varying from one technology to another, are the backbone of wireless communication systems, handling everything from signal synchronization and network discovery to data transmission and control messaging. The table below provides an insightful comparison of the physical layer channelization across a range of wireless technologies, including Bluetooth, Wi-Fi, CDMA, GSM/GPRS, WCDMA, LTE, and 5G/NR. This comparison highlights the evolution and specialization of channel use and functionality, reflecting the diverse requirements and capabilities of each technology.

• Reading the table
• The three jobs every technology has to do
• What changes from GSM to NR

Reading the table

The table sets seven technologies against one another, from Bluetooth to 5G NR. Read it down the first column to follow a single technology, and across the second column to compare how each one solves the same problem. The second reading is the more useful of the two.

Each row gives one purpose and the channels that serve it. A technology occupies as many rows as it has distinct purposes, which is why the entries in the first column span several rows at a time.

• The first column names the technology, and it spans every row that belongs to that technology.
• The second column names the purpose, and the same few purposes repeat all the way down the table.
• The third column names the channels themselves, in each technology's own vocabulary.

One cell is empty. The Bluetooth row for Control and Data Channel carries no entry in the Channels column, so that gap is still to be filled.

The three jobs every technology has to do

The Purpose column is shorter than it first looks. Seven technologies fill it with only three recurring entries, plus one outlier. Every system in the table has to be found, has to announce what it is, and has to carry traffic, and the three purposes line up with those three jobs.

The first job is being found. A device that has just powered on knows nothing about timing, frequency or identity, so something has to arrive that it can lock onto with no prior knowledge. Bluetooth uses Inquiry and Page Channels, Wi-Fi uses Beacon Frames and Probe Request and Response, CDMA uses the Pilot Channel, and every cellular row uses a sync channel. The names differ and the job does not.

The second job is announcing the parameters. Once a device has locked on, it still needs the identity of the network, the bandwidth and the access rules before it can transmit anything. GSM/GPRS, WCDMA, 4G/LTE and 5G/NR each give this a Broadcast Channel row of its own.

Three rows carry no broadcast entry, and that is not an omission. In Wi-Fi the Beacon frame does both jobs at once. A device discovers the network from that frame, and the same frame carries the network's parameters. Bluetooth works the same way, with the inquiry response carrying the device details.

The third job is carrying control and traffic, and every technology in the table has a Control and Data Channel row. That row is the one that grows, because it holds the scheduling, the feedback and the payload together.

The outlier is the Wi-Fi row for DFS Channels, which serves no communication purpose at all. DFS exists because the 5 GHz band is shared with radar, and a device has to vacate a channel once it detects one. No cellular row carries anything equivalent, because the cellular technologies listed here run in licensed spectrum where no such obligation applies.

What changes from GSM to NR

Reading the third column down the cellular rows shows two changes, and neither of them is about adding more channels. The naming convention changes first, and then the list of channels gets shorter rather than longer. Both changes say something about how the design was simplified.

GSM names bursts. Its entries read Synchronization Burst, Frequency Correction Burst, Access Burst and Normal Burst, with the logical channels given in brackets after each one. A single Normal Burst carries TCH, SDCCH, SACCH, FACCH, BCCH or PCH, depending on what the network has scheduled. The burst is the physical thing, and the channel names ride on it.

WCDMA onwards names the physical channel directly. P-CCPCH, PDCCH and PUSCH are channels rather than burst shapes, and the mapping from logical channel to physical channel moved out of the name and into the specification.

The second change appears between the last two rows. 4G/LTE lists six channels for control and data, namely PCFICH, PHICH, PDCCH, PDSCH, PUCCH and PUSCH. 5G/NR lists four, and the two that went are PCFICH and PHICH.

Both removals replaced a signalled value with a configured one. PCFICH told the UE how many symbols the control region occupied in each subframe. NR configures a CORESET instead, so the answer is already known and needs no channel of its own. PHICH carried the acknowledgement for an uplink transmission. NR schedules any retransmission explicitly in the downlink control information, so the dedicated channel became unnecessary.

One entry is worth noticing because it appears twice. PDSCH sits in the Broadcast row and in the Control and Data row, for 4G/LTE and for 5G/NR alike. The system information blocks travel on the same shared channel as user traffic, so broadcasting is a function here rather than a dedicated channel. Only the MIB keeps a channel to itself, on PBCH.