All posts by Azar

WHAT IS THE PURPOSE OF THE PHY LAYER?

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Physical channels are the ones over which information is transmitted in air interface as bits and symbols. From the protocols perspective, Physical layer is Layer 1 protocol. You can see from the visualization below, Physical layer is performing coding, modulation, antenna and resource selection. Support of Physical Layer to Channels: Take a look at the […]

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WHERE ARE DATA FLOW AND MULTIPLEXING USED IN LTE AIR INTERFACE? OR HOW DO PROTOCOLS OPERATE IN LTE AIR INTERFACE?

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First, you need to have understanding of LTE Air Interface protocols. Once you have that understanding, it is easy to trace an IP packet from user plane perspective, passing through each of the protocols all the way down to physical layer to understand the role of each protocol layer. For your convenience, I have listed […]

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WHAT IS THE PURPOSE OF THE PDCP LAYER?

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In order to answer this question, take a look at the picture below. I have shown PDCP protocol both in Control and User plane protocol stack. The PDCP protocol performs the following Supports Robust Header Compression (ROHC) and decompression of user plane data. PDCP supports ciphering of user plane data and control plane data (NAS […]

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WHAT IS THE PURPOSE OF THE RLC LAYER?

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In order to answer this question, take a look at the picture below. I have shown RLC protocol both in Control and User plane protocol stack. Modes of RLC Protocol The RLC protocol supports three modes of operation An Unacknowledged Mode (UM) An Acknowledged Mode (AM) Transparent Mode (TM). Whether UM or AM is used, […]

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HOW DOES HARQ OPERATE?

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The Hybrid ARQ (HARQ) protocol in MAC layer operates such that the protocol uses multiple stop-and-wait hybrid ARQ processes. The motivation for this type of protocol is to allow continuous transmission, which cannot be achieved with a single stop-and-wait scheme, while at the same time having some of the simplicity of a stop-and-wait protocol. The […]

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