Channels changes in terms of LTE and 5G

Hello Experts.

What does channels indicate in terms of LTE/5G?

I mean, when I say channels like PDCCH, PUSCH what does it really indicate?

I am not expecting answer like these are in available resource grid etc.

When we say PHICH channel was available in LTE for HARQ feedback in DL for UL data, but in 5G we don’t have this channel.

So what does this mean?

What changes they have made in 5G architecture to remove this channel etc.

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Channels are like logical lanes a specific information is exchanged.

Some lanes are open for all (RACH / PRACH), some are controlled (PDCCH, PDSCH).

Between technologies, entire architectures are revised to improve and optimise so some lanes are closed.

A better mechanism or new lanes are open.

Thanks, this is great, but more of layman’s term.

I am looking for more accurate answers. :slight_smile:

Are you asking specifically for PHICH?

Thought you were asking generic reply…

Both, actually.

I mean, when I say PDCCH, is the L1 who does some intelligence because for DL data gNB has just sent the data to L1, rest L1 has to do.

PDCCH is still there in 5G.

For PCFICH, we have CORESET in 5G configuration which helps with information to decode PDCCH .

PHICH was used for HARQ but here in 5G we have asynchronous HARQ concept both in DL and UL so some additional parameters are being used which UE used for feedback about downlink transmission.

For UL retransmission UE gets indirectly by receiving UL grant again with same HARQ ID without NDI toggle with new RV.

Sorry dear, another great answer, but still not exactly the answer I am looking for. :slight_smile:

(I am already aware of these concepts)

In the name of K0, K1,K2, Params, it can be done.

Correct, and I agree (Thanks, another great reply).

But as i sadi, I am aware of these things.

Let me ask in this way: when I say channels, I know these are logical channels, so what does each channels represent, does they represent a part of bandwidth or freq?

Let’s say I have system / board, which support frequency from 1920 MHz-1980 MHz, so for e.g 1920 Mhz is for PRACH, 1920.1 is for PHICH, 1920.2 is for logical channel x, 1920.3 is for logical channel y so on and so forth?

The meaning of channel has different meanings according to the layers.

Logical, transport and physical.

Internal software logical pipe communication between layers ex. MAC to RLC (Logical), PHY to MAC (transport) and PHY to air (Physical).

Researchers and PHY software developers know more from Air interface view, not from Protocol view.

You can’t fix the location in frequency and time domain.

This is my question. :slight_smile:

If someone can elaborate more on this.

In LTE and 5G, “channels” refer to specific logical, transport, and physical channels used for communication between the base station (eNodeB or gNodeB) and the user equipment (UE). Each channel has a specific role in managing data transmission, control information, and other essential communication functions. Here’s what some key channels represent:
PDCCH (Physical Downlink Control Channel): Used for transmitting control information necessary for decoding the PDSCH (Physical Downlink Shared Channel) and other downlink channels.
PUSCH (Physical Uplink Shared Channel): Used for carrying uplink user data from the UE to the base station.
PHICH (Physical Hybrid ARQ Indicator Channel): Used in LTE for carrying HARQ (Hybrid Automatic Repeat Request) acknowledgments for uplink data transmissions.

Changes in 5G Architecture:
In 5G, the architecture has evolved to provide more flexibility, efficiency, and support for a wider variety of use cases compared to LTE. One of the key changes is the simplification and optimization of channels. Here’s what happened to PHICH and other notable differences:
Elimination of PHICH: Reason: In LTE, PHICH was used to send HARQ feedback for uplink transmissions. This required a dedicated channel and additional signaling overhead.5G Approach: 5G NR (New Radio) uses different mechanisms for HARQ feedback. Specifically, HARQ feedback is now embedded within the PUCCH (Physical Uplink Control Channel) or PUSCH. This reduces the need for a dedicated downlink channel like PHICH and simplifies the design.Enhanced Flexibility with PUCCH:In 5G NR, the PUCCH has been enhanced to carry various types of control information, including HARQ acknowledgments, scheduling requests, and CSI (Channel State Information) reports. This consolidated approach reduces the need for separate channels and improves efficiency.Increased Use of Dynamic Scheduling:5G employs more dynamic and flexible scheduling for uplink and downlink transmissions. The use of DCI (Downlink Control Information) sent via PDCCH allows for more adaptable and efficient resource allocation.Control and Data Separation:5G NR emphasizes the separation of control and data planes, which allows for better handling of different types of traffic and improves overall network performance.Summary:In LTE, specific channels like PHICH were used for certain tasks such as providing HARQ feedback for uplink transmissions. In 5G, the architecture has been streamlined, and functionalities have been consolidated into fewer, more versatile channels like the PUCCH and PUSCH. This reduces overhead and complexity while enhancing flexibility and efficiency. The removal of PHICH and the integration of HARQ feedback into existing channels is a prime example of these improvements.

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