WHAT IS THE PURPOSE OF THE MAC LAYER IN LTE?

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The MAC layer functionalities in LTE are listed below such as: Hybrid ARQ (HARQ) Priority handling (scheduling) Transport format selection Discontinuous Reception (DRX) control etc. MAC Layer Support The MAC layer does not support in-order delivery to Radio Link Control (RLC). HARQ re transmissions lead to MAC Protocol Data Units (PDUs) being received in a […]

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WHY DO WE NEED UPLINK TIME-ALIGNMENT IN RRC CONNECTED MODE?

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One of the reasons we need to maintain time alignment in the uplink is to maintain orthogonality in the uplink. Secondly, RRC Connected state supports Discontinuous Reception (DRX) / Discontinuous Transmission (DTX). In uplink transmission sometimes the term discontinuous UL transmission is used which means UL time alignment (synchronization) has been lost. If a UE has been […]

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WHAT ARE THE USER PLANE PROTOCOL STACK AND FUNCTIONALITY OF THOSE PROTOCOL LAYERS?

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LTE user plane is shown in the figure below. LTE radio interface architecture consists of UE and eNodeB. The resulting user plane protocol stack and the protocols involved in the LTE radio interface are shown in figure below. In LTE user plane, the four radio protocol layers are terminated in the eNodeB. The brief functionalities […]

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WHAT IS THE MEANING OF THE RANDOM-ACCESS BACK-OFF PROCEDURE?

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In the incidence of a lot of users sending random access attempts, too many random attempts at the same time can result in Random Access Overload. For the event of Random Access Overload, a Random Access Backoff procedure is supported. This procedure prevents immediate new Random Access attempts. The UE waits until a back-off timer […]

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WHAT IS THE PURPOSE OF CONTENTION-FREE RANDOM ACCESS PROCEDURE?

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For cases where the network knows in advance that a particular UE will perform a Random Access Procedure to acquire uplink synchronization, a dedicated preamble is reserved and assigned to the UE under consideration. EXAMPLE Dedicated preamble assignment for handover (HO) is handled by RRC, whereas preamble assignment for DL data arrival is handled by […]

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