CDN - An opportunistic Scheduling Scheduling Scheme with a Minimum Date-Rate Guarantees for OFDMA

1. An Opportunistic Scheduling Scheme
with Minimum Data-Rate Guarantees
for OFDMA
George Suveti
Cellular Data Networks

2. OFDM & OFDMA
OFDM
Orthogonal frequency-division multiplexing (OFDM) is a method of encoding digital data
on multiple carrier frequencies. OFDM has developed into a popular scheme for
wideband digital communication, used in applications such as digital television and audio
broadcasting, DSL Internet access, wireless networks, powerline networks, and 4G
mobile communications.
OFDMA
Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user version of the
popular orthogonal frequency-division multiplexing (OFDM) digital modulation scheme.
Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual
users. This allows simultaneous low data rate transmission from several users.

3. OFDM & OFDMA

4. RELATED WORK
Opportunistic scheduling
In order to provide higher system capacity in a multiuser wireless environment by taking advantage of
instantaneous channel variations and giving transmission priority to the users with better channel
conditions. This is referred to as multiuser diversity and is the basis of opportunistic scheduling (OS).
OS schemes adopt a cross-layer approach to medium access control (MAC) packet scheduling by
making use of the channel state information (CSI) of each user, retrieved at the physical layer.
Techniques of opportunistic scheduling:
- schedule the users with better channel quality for transmission
- Round Robin, independently of the channel conditions form of
- proportional fair algorithms, aims at assuring a degree of fairness on a long term scale
(e.g. choose for transmission, at each time-slot, the user with the highest ratio between its
instantaneous channel capacity and its average data rate.

5. Goal
To design a scheduling algorithm for a heterogeneous traffic OFDMA-based system that
will guarantee a minimum average (on a system-set time scale) data-rate for each user,
based on classes-of-service, while using opportunistic scheduling in order to maximize
the system spectral efficiency.
The algorithm considers the variations of the channel quality for each user as
compared to the average value over the considered time window, and try to schedule for
transmission, at each time-slot, the users that have greater than average channel
quality.
SCHEDULING ALGORITHM

6. SCHEDULING ALGORITHM

7. SIMULATION RESULTS

8. SIMULATION RESULTS

9. SIMULATION RESULTS

10. CONCLUSIONS
The proposed algorithm, by leveraging multiuser diversity, outperforms classic OS
schemes due to its ability to provide minimum data-rate guarantees for different
classes of service, while at the same time provides a high system throughput.
The hardness of the constraints as well as the level of the introduced delays can be
controlled by modifying the size of the time window over which scheduling is performed.
The inverse proportional relationship between the level of the data-rate guarantees and
the system throughput(or spectral efficiency) has been evidenced.
Further work
Extend the heuristic in order to take into account queue information and thus provide
delay guarantees.