LTE Packet Scheduling.pdf

LTE cellular networks utilize packet scheduling algorithms to manage radio resources in both downlink and uplink transmissions. Downlink transmission uses Orthogonal Frequency Division Multiple Access (OFDMA), while uplink transmission uses Single Carrier – Frequency Division Multiple Access (SC-FDMA). The main difference between OFDMA and SC-FDMA is the way they schedule users, with OFDMA allowing multiple users to share the bandwidth at the same time.

Key packet scheduling algorithms in LTE include:

Max Carrier-to-Interference (C/I)
Round Robin (RR)
Proportional Fair (PF)
Earliest Deadline First (EDF)
Modified EDF-PF
Modified-Largest Weighted Delay First (M-LWDF)
Exponential Proportional Fairness (EXP-PF)
Token Queues Mechanism
Packet Loss Ratio (PLR)
Quality Guaranteed (QG)
Opportunistic Packet Loss Fair (OPLF)
Low Complexity (LC)
LC-Delay
PF-Delay
Maximum Throughput (MT)
First Maximum Expansion (FME)
* Adaptive Resource Allocation Based Packet Scheduling (ARABPS)

These algorithms have different characteristics, formulas, and suitable conditions for use. The choice of algorithm depends on the specific requirements of the network and the users. The LTE scheduling process involves the interaction between users and the scheduler, with the scheduler allocating radio resources based on a predefined metric.

The use of OFDMA in downlink transmission improves spectrum utilization and helps avoid narrow-band fading and interference. SC-FDMA is used in uplink transmission due to its low Peak-to-Average Power Ratio (PAPR), low complexity, and ability to provide frequency diversity.

The performance of SC-FDMA is affected by the mapping mode used, with two main types of mapping modes: distributed and localized. The localized mode achieves multi-user diversity in frequency-selective channels, but requires Channel State Information (CSI) to map data into the best adjacent symbols. The distributed mode provides inherent frequency diversity, but may lose user diversity.

Overall, the choice of packet scheduling algorithm and mapping mode depends on the specific requirements of the network and the users, and the trade-offs between different performance metrics such as throughput, delay, and fairness.