Utilizing WiMAX mesh mode for efficient IPTV transmission
Murat Ozyurt, Seckin Ulug, Tuna Tugcu
In proceedings of MSWiM 2010 , The 13-th ACM International Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems, October 17-21, 2010 Bodrum, Turkey
Boğaziçi University, Computer Engineering Department Computer Networks Research Laboratory
Introduction
WiMAX provides high-speed data within base-station coverage, using concentric cells with varying modulation based on signal quality. While users demand high data rates, factors like distance, multi-path fading, and interference limit high-modulation efficiency. In urban environments, non-line-of-sight (NLOS) conditions, caused by obstacles, require using such lower-efficiency connections for most users.
Figure: Concentric modulation zones in a WiMAX cell
To support high-bit-rate IPTV in this context, a mesh-mode approach is proposed where "two-hop" nodes, suffering from low-quality links, receive content relayed by nearby "one-hop" nodes that enjoy high-capacity connections to the base station. Unlike IEEE 802.16j, which focuses on coverage expansion, this mesh-mode approach targets improving channel quality for underserved users in dynamic environments, which is more cost-effective than static, high-cost relay stations.
The proposed system also considers 4x4 MIMO, allowing a single base station to potentially support up to 50 distinct 6 Mbps IPTV channels. The system accounts for increased load when relay nodes re-transmit content to two-hop nodes. Simulation results, to be discussed, demonstrate that by leveraging spatial diversity, shared channels (multicast), and direct connections, the system manages to meet channel demands while maintaining efficient bandwidth usage. Note that three-hop connections are excluded due to latency constraints on IPTV.
This paper proceeds with the problem formulation, proposed solutions, simulation results, and future work in the subsequent sections.
IPTV Over WiMAX
Definitions
| Term | Definition |
|---|---|
| r | Traffic requirement of a TV channel in terms of bits-per-second. |
| O | Total number of one-hop nodes in the network. |
| T | Total number of two-hop nodes in the network. |
| F | Framelength of a single burst of an IPTV channel in terms of bits. |
| CBS | Base station modulation capacity in terms of bits-per-second. |
| Ci | Modulation capacity of the ith one-hop node in terms of bits-per-second, where i is an element of [1, 2, …, O]. This value is equal to CBS for all one-hop nodes throughout this paper. |
| K | Worst-case duration of a frame schedule iteration. |
| Ks | Worst-case duration of a frame schedule iteration when there is only one TV channel transmission for the entire network. |
| Ksu | Worst-case duration of a frame schedule iteration when there is only one TV channel transmission for the entire network and one-hop nodes relay with single modulation. |
Node Calculator
Figure: Node calculation flow analysis
Worst-Case Problem
For a given O and T pair, the minimum bandwidth requirement at the base-station is defined by the absolute capacity limit of the shared channel. Conversely, the minimum bandwidth requirement between one-hop and two-hop nodes is dependent on localized structural interference and physical node placement parameters.
Figure: Round-robin transmission scheme
Single TV Channel Transmission
Figure: Single-channel simulation flow path
Simulation Setup
The IPTV over WiMAX simulation provides an estimation of runtime service configurations. Some configuration parameters evaluate the mathematical probability of transient events, while other settings specify baseline architecture limits for the performance evaluation framework.
| Parameter | Value | Description |
|---|---|---|
| Channel Count | 1000 | Number of IPTV channels available in the system catalog. |
| Channel Bandwidth | 6 Mbps | Bitrate requirement per TV channel (represented as r). |
| Frame Length | 300 Kbits | Size of a discrete stream frame chunk (represented as F). |
| Simulation Duration | 180 min | Total programmatic execution window in minutes. |
| One-Hop Nodes | 100 | Initial pool of primary receiver nodes with direct BS visibility. |
| Two-Hop Nodes | 50 | Initial baseline volume of shaded secondary relay clients. |
| Probability of a New Node | 0.03 | Likelihood per elapsed second that an arbitrary new node joins. |
| Probability of Leaving | 0.03 | Likelihood per second that an active subscriber leaves the cell. |
| Probability of Finding a Transfer Node | 0.10 | Probability a orphaned two-hop node seamlessly adopts a new host if its original one-hop anchor drops out. |
| Probability of Two-Hop Connection | 0.30 | Chance a freshly registered user requires an indirect multi-hop routing channel. |
| Probability of Changing Channel | 0.06 | The metric modeling user channel-zapping behaviors each second. |
| Probability of Collision At Two-Hop Nodes | 0.10 | Chances that adjacent multi-point mesh relays create packet overlap. |
The simulation runs continuously through the specified timeline window. It triggers dynamic mutations inside the active physical network layout via scheduled object additions, teardowns, and route transitions while gathering runtime trace metrics like aggregate frame miss boundaries and inter-frame arrival variance profiles.
Simulation Results
WiMAX dynamically selects different modulation configurations depending on active link path conditions. The scheduler always prioritizes higher-capacity modulations to optimize performance metrics. However, deep fading or rising bit error rates force fallbacks to lower-efficiency modulations to avoid complete session loss. While advanced schemes like QPSK, 16-QAM, 64-QAM, and 256-QAM multiplex multiple streaming profiles, baseline raw operational metrics must be balanced against high user-density urban IPTV layouts.
| Modulation | Coding Rate (cr) | Rb (Mbps) |
|---|---|---|
| BPSK | 1/2 | ~75 |
| QPSK | 1/2 | ~150 |
| QPSK | 3/4 | ~224 |
| 16-QAM | 1/2 | ~299 |
| 16-QAM | 3/4 | ~449 |
| 64-QAM | 1/2 | ~399 |
| 64-QAM | 2/3 | ~532 |
| 64-QAM | 3/4 | ~673 |
| 64-QAM | 5/6 | ~748 |
| 256-QAM | 1/2 | ~532 |
| 256-QAM | 3/4 | ~898 |
| 256-QAM | 5/6 | ~997 |
Air-Link Utilization Analysis
| One-Hop \ Two-Hop | 10 Nodes | 30 Nodes | 50 Nodes | 70 Nodes | 90 Nodes |
|---|---|---|---|---|---|
| 10 Nodes | 47.8% | 52.2% | 56.6% | 63.2% | 75.1% |
| 30 Nodes | 50.6% | 61.4% | 76.4% | 84.5% | 92.1% |
| 50 Nodes | 72.8% | 80.8% | 89.7% | 94.0% | 97.3% |
| 70 Nodes | 89.1% | 95.5% | 97.4% | 98.9% | 99.4% |
| 90 Nodes | 96.3% | 98.3% | 99.9% | 99.7% | 99.9% |
Three-hour simulations replicated across 100 iterations utilized a baseline 300 Mbps MIMO link setup to study density expansion behavior. System loading tracks proportionally with node numbers. For example, layouts like 70×10, 50×50, or 30×70 maintain optimal headroom. Exceeding these thresholds introduces total allocation saturation, though inter-frame arrival variance remains statistically acceptable.
Figure: Utilization trends across different network scaling profiles
Delay and QoS Evaluation
Heavy traffic conditions reveal rigorous performance demands. A 6 Mbps channel streaming 300 Kbit frame sizes dictates an output frequency of 20 frames per second, creating precise 50-millisecond window slices. Although human optical perception limits do not typically isolate delays below 100 ms, we conservatively enforce a strict 50 ms safety threshold for absolute delivery tolerance.
| Node Profile | Configuration | No Delay | < 20 ms | 20–50 ms | 50–100 ms | 100–125 ms | > 125 ms |
|---|---|---|---|---|---|---|---|
| For One-Hop Nodes | 10 by 50 | 84.85% | 12.78% | 2.37% | 0.00% | 0.00% | 0.00% |
| 50 by 30 | 52.44% | 28.29% | 19.03% | 0.24% | 0.00% | 0.00% | |
| 90 by 50 | 51.86% | 4.48% | 16.35% | 27.05% | 0.26% | 0.00% | |
| For Two-Hop Nodes | 10 by 50 | 63.46% | 26.32% | 8.30% | 1.74% | 0.18% | 0.00% |
| 50 by 30 | 47.90% | 25.88% | 25.44% | 0.40% | 0.35% | 0.03% | |
| 90 by 50 | 54.84% | 2.94% | 12.46% | 28.88% | 0.28% | 0.60% |
Figure: Frame delay distribution breakdown
Figure: Average inter-frame jitter profiles measured at primary hops
| One-Hop \ Two-Hop | 10 Nodes | 30 Nodes | 50 Nodes | 70 Nodes | 90 Nodes |
|---|---|---|---|---|---|
| 10 Nodes | 3 / 4 | 2 / 18 | 9 / 15 | 16 / 29 | 22 / 44 |
| 30 Nodes | 1 / 14 | 8 / 10 | 15 / 22 | 20 / 33 | 29 / 49 |
| 50 Nodes | 8 / 8 | 16 / 19 | 27 / 34 | 33 / 46 | 42 / 61 |
| 70 Nodes | 19 / 19 | 27 / 31 | 37 / 44 | 49 / 61 | 60 / 77 |
| 90 Nodes | 34 / 33 | 41 / 45 | 57 / 63 | 63 / 74 | 80 / 95 |
Figure: Secondary mesh path delivery lag measurements
Statistical Synthesis
- 10 One-Hop / 50 Two-Hop Setup: Delivers 84% (First-Hop) and 63% (Second-Hop) zero-delay frames, tracking well within expected tolerance profiles.
- 50 One-Hop / 30 Two-Hop Setup: Drops zero-delay delivery rates to 52% and 47%, shifting remaining traffic smoothly into safe, manageable buffer brackets.
- 90 One-Hop / 50 Two-Hop Setup: Maintains baseline delivery ratios but surfaces critical capacity fatigue, pushing ~28% of total runtime frames beyond acceptable QoS margins.
Conclusion
In this paper, a WiMAX solution based on mesh mode operation is proposed for efficient IPTV distribution. Instead of multicasting all IPTV channels with more robust but less spectral efficient modulations (such as QPSK using PMP mode), utilizing mesh mode operation and relaying enables the use of less robust but more spectral efficient modulations (such as 256-QAM). As a result, this solution can serve more IPTV channels compared to single multicasting in PMP mode. While alternative relaying methods exist—such as IEEE 802.16j-WiMAX with relay stations operating in PMP mode—WiMAX mesh mode operation holds the advantage of structural adaptability to changing traffic requirements and dynamic topology.
Based on the simulation results presented in this paper, IPTV over WiMAX mesh mode supports a wide range of multiple users to receive dedicated transmissions via a one-hop node if not directly from the base station. For a simulation with a base station transmission capacity of 300 Mbps and 1000 available IPTV channels, it is possible to generate a schedule for 50 directly connected nodes and 30 indirectly connected nodes with reasonable, tolerably safe inter-frame delays.
If the total volume of one-hop nodes and two-hop nodes remains below 120, the aggregate network utilization stays below 1.00. This operational baseline allows a higher number of subscriber nodes to be safely supported in urban areas suffering from severe signal propagation obstructions and complex relay demands. However, for IPTV channels requiring higher bandwidth profiles, baseline modulation capacities must scale accordingly; otherwise, high-capacity user demands will create systemic resource deficits, causing other neighboring clients to suffer poor quality of service (QoS).
Future Work
- Parallelism Optimization: Implement an advanced parallel slot-allocation algorithm that maps colliding one-hop transmissions onto non-overlapping concurrent streams, further decreasing dedicated time slot requirements.
- Channel Modeling Integration: Replace the random relay-to-node mapping framework with predefined, realistic signal propagation models (such as Rayleigh or Rician fading channels) to better align with practical deployment environments.
Acknowledgment
This work is partially supported by the Scientific and Technical Research Council of Turkey (TÜBİTAK) under grant number 108E101.