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References

[1] A. Thakur, S. De and G. -M. Muntean, "Co-Channel Secondary Deployment Over DTV Bands Using Reconfigurable Radios," in IEEE Transactions on Vehicular Technology, vol. 69, no. 10, pp. 12202-12215, Oct. 2020, doi: 10.1109/TVT.2020.3016172.

[2] A. Thakur and S. De, "On Deploying Secondary Networks in Co-Channel Bands with DTV Networks," in IEEE Transactions on Vehicular Technology, vol. 71, no. 7, pp. 7791-7804, July 2022, doi: 10.1109/TVT.2022.3168227.

[3] OpenStreetMap contributors, “Planet dump retrieved from https://planet.osm.org ,” https://www.openstreetmap.org , 2017

Department of Electrical Engineering

Coexistent communication over TV broadcast band

Anshul Thakur, Rajrshi Dubey & Swades De^*

Result

#Communication Technologies

Option A: Using Millimeter waves

Poor propagation characteristics
Requires dense deployment of cells
Therefore, unfit for sparsely populated areas due to the poor economy of scale

Option B: Reusing TV broadcast bands (470 MHz to 862 MHz UHF)

Excellent propagation characteristics
Excellent in-building penetration
Highly underutilized, particularly post analogue-to-digital switchover

TV Grey Spaces (TVGS): Over-the-Air (OTA) TV ownership is low, and viewership fluctuates between 7.6% during midnight to 60% during prime time No receiver ⇒ no interference
TV Black Spaces (TVBS): High Signal to Noise (SNR) ratio inside the coverage area creates excess interference margin at DTV receivers

No temporal holes in the DTV broadcast transmission on a small time scale
Mostly unidirectional, all victims (receivers) are hidden
Fixed transmission parameters, no adaptation
Large coverage radius
Current DTV standards, such as DVB-T, DVB-T2, ATSC 3.0 based on Orthogonal Frequency Division Multiplexing (OFDM)
Other compatible OFDM systems can exploit architectural differences in timing, frequencies, power, and how OFDM signals interact

SECONDARY COGNITIVE RADIO SYSTEM OPERATION

Figure out/estimate locations of DTV receivers

Figure out/estimate interference impact at DTV receivers

Compute operating parameters

Problem: - No feedback from DTV receivers

Step 1

Step 2

Step 3

Exhaustive Parameter Search (EPS) algorithm^[1]

Interference on DTV receiver from a secondary transmitter can be reduced by: -

Using lower transmit power
Reducing temporal occupancy of the secondary signal
Varying the spectral overlap between primary and secondary systems

To localize the most vulnerable/critical DTV receiver for each secondary transmitter as accurately as possible

Minimal information: statistical estimates of population/household density, TV Ownership rate
Geographical information: geospatially tagged map of area marking houses, TV Ownership rate
Complete information: Exact (average) signal conditions at the DTV receiver are known

Using statistical path-loss models
Using data-driven approach: Kriging interpolation – Signal power & interference at the DTV receiver is predicted based on the data measured by secondary nodes

Exhaustive Parameter Search (EPS) algorithm^[1]

Demographic estimates^[2]

Geospatial Maps^[2]

Fig 1. The concept of TV Black Space (TVBS) and TV Gray Space (TVGS).

Fig 2. Channel access opportunity - existing paradigm.

Fig 3. Channel access opportunity - cognitive radio paradigm.

Fig 4. Symbol duration differences between DVB-T2, LTE, 802.11 (WiFi).

Fig 5. Blanking a controlled amount of subcarriers for some OFDM symbol slots by the secondary CR system (duration T^(s)) during a DTV symbol slot (useful duration T_u^(D)) can reduce the interference experienced by the DTV receiver

Fig 6. Experimental setup to study the effects of co-channel secondary transmission on DTV reception.

Fig 7: SINR variation at the DTV receiver with varying spectral overlap for LTE-like secondary transmission at different received powers of the secondary signal. Symbol period T(S) = 66.6 µs, subcarrier spacing = 15 kHz.

Figure 8: SINR variation at the DTV receiver with varying time occupancy for LTE-like secondary transmission at different received powers of the secondary signal. Symbol period T(S) = 66.6 µs, subcarrier spacing: 15 kHz, maximum secondary time slots per DTV OFDM symbol = 7.

Table II: Power ratios required to maintain interference thresholds at a DVB-T2 receiver with interference from a secondary network node using LTE-like transmission.

Fig 9: Variation of secondary coverage range at minimum supported data rate (4.4 kbps) as the distance of secondary BS increases from the DTV transmitter for urban clusters, Population density (λ = 400km^-2).

Fig 10: Variation of DTV receiver outages at minimum supported data rate (4.4 kbps) as the distance of secondary BS increases from the DTV transmitter for Urban clusters, Population density (λ = 400km^-2).

Fig 11: Map of buildings in a metro city and adjoining areas. Approximately 1.5 million data points (marked blue) in 40km2 area. DTV Transmitter is on the top-left.

Fig 12: Secondary uplink coverage range computed for the given buildings map with Kriging interpolation for O(c) = 0.6.

Parameter	Value
Downlink Bandwidth	8 MHz
Downlink Frame Duration	250 ms
Path-Loss exponent	2.7
Shadowing coefficient	9.6 dB
DTV outage threshold	0.01
CR outage threshold	0.05

Conclusions

Interpolation method used (Kriging) allows substantially better signal estimates compared to statistical path-loss models

Not much change in coverage

Significant improvement in outage performance (from 0.08 to < 0.01)

Use of geospatial maps along with Kriging allows heterogeneity of population dynamics to be incorporated into secondary network operation

Significantly improves coverage in sparsely populated areas)

Better estimation ⇒ better coexistence

Table I. Simulation parameters and values

Step 3: Compute operating parameters

Step 1: Figure out/estimate the locations of DTV receivers

Step 2: Figure out/estimate interference impact at DTV receivers

Proposed methods and algorithms

Features of TV broadcast transmission: -

Introduction

Increasing the population of wireless devices will increase strain on scarce broadband resources.

Coexistent communication opportunities in TV broadcast band

TVWS based approach (geolocation) is transmit centric, but the victims of interference are DTV receivers
No service inside DTV coverage region creates large, unserviced geographies
Important to find coexistent communication opportunities in TV Black & Grey spaces

Technology Readiness Level

Experimentally verified interference reduction at active DTV receiver nodes using off-the-shelf DTV receivers using the proposed method
Geospatially tagged information can be obtained from opensource collaborative projects, such as OpenStreetMaps^[3], or from commercial projects, such as Google Earth
Feasibility study of secondary receiver in the ATSC 3.0 broadcast band is the subject of ongoing research

Industrial Significance

Reliable and ubiquitous cognitive secondary networks remove entry barriers for new and small players, particularly for IoT devices

Doesn’t require explicit spectrum licenses

Doesn’t require explicit cooperation agreements and information sharing with the DTV networks

DTV band deployment leads to greater coverage with a lesser number of devices, thus leading to a reduction in Capex and Opex
Overcomes poor economies of scale and creates new markets in currently underserved, hard-to-reach areas

Abstract

A novel approach for coexistent communication between an active Digital TV (DTV) broadcast and an OFDM based cognitive secondary network
Works in the absence of TV White Spaces also
Non-intrusive method that is attuned to the characteristics and limitations of Digital TV broadcast architecture
Exploits the structure of DTV transmission to reduce interference impact while transmitting higher power
Enables ubiquitous secondary network access and manages interference levels dynamically instead of completely restricting access
Uses data-driven approach by combining signal level readings from the secondary network nodes to interpolate signal conditions at the DTV receivers to estimate interference impact
Meets stringent outage requirements of a DTV network while also providing reliable connectivity across a low data rate secondary network

Coexistent communication opportunities in TV Black & Grey space:

TV White space (TVWS): Region where TV service is unavailable
TV Grey space (TVGS): Region where TV service is available, but the TV receiver is absent/off
TV Black space (TVBS): Region where TV service is available, and the TV receiver is on