Letters

Portable Wireless System for DigitalVideo Transmission
Tomotaka Yoshie†, Hideyuki Maruyama, and Toshio Saito
Abstract
A portable wireless system that enables digital video transmission in a simple fashion has been developed at NTT Access Network Service Systems Laboratories to provide a temporary TV terminal link
between a TV terminal station operated by NTT Communications Corporation and a TV station. Thissystem enables stable digital video transmission even under severe interference conditions. For easierportability, its volume and weight have been decreased compared with portable wireless systems for analog video transmission that NTT developed in the past.

1. Introduction
With the start of terrestrial digital broadcasting
approaching, analog equipment for broadcasting isbeing replaced by digital equipment. Demand isgrowing for HDTV (high-definition television) classhigh-quality video delivery based on high-speed
Internet access via optical fiber, and we also expect anincrease in demand for a delivery method for contents
gathering systems.
So far we have developed portable wireless systems
only for analog video transmission. Recently, we
have developed a portable wireless system for transmitting digital video that can be set up anywhere in asimple manner.
2. System overview
2.1 Application
This system will be applied to digital TV relay services that NTT Communications intends to provide tobroadcasting stations. Figure 1 illustrates the application of this system. The network for digital TV relay
service comprises relay links interconnecting TV terminal stations and terminal links connecting TV terminal stations with the broadcasting stations. Our
system is designed for the TV terminal links. It can be† NTT Access Network Service Systems Laboratories
Yokosuka-shi, 239-0847 Japan
E-mail: yoshie@ansl.ntt.co.jp

74used as a substitute link connecting the TV terminal
station and the TV station when optical fiber TV terminal links are disconnected by a disaster, for example. It can also provide temporary TV terminal links
connecting the site of a topical event to a TV terminal
station according to the transmission needs.
2.2 System configuration and development
concept
This portable wireless system uses the 11- or 15GHz band to transmit digital video in one direction.
The transmitter is composed of four units: i) a transmission control unit that processes and modulates aninput signal; ii) a transmitting radio unit that performs
frequency up-conversion, amplification, and transmission of the signal as a radio wave; iii) an antenna;and iv) a tripod that supports the transmitting radiounit. The receiver is also composed of four units: i) a
receiving radio unit that receives and amplifies theradio wave sent from the transmitter; ii) an antenna;iii) a reception control unit that performs signal processing such as demodulation; and iv) a tripod that
supports the receiving radio unit. The system configuration is shown in Fig. 2. We focused on the following development points.
• High-quality video transmission such as HDTV
• Quick setup for transmission• Portability (compact and lightweight)• Operation under various propagation conditions• Multi-purpose design
The main specifications of the prototype and comNTT Technical Review

Letters

Digital TV relay service (provided by NTT Communications)• Service starting this year
• Provided by ATM network+this system+satellite
communications system

Transportableearth station

Satellite
communications
systemBroadcastingstationRecovery of
TV terminal link

Communications
satellite

Television
terminalstation
This system

VideoMUXTV
terminal link
Television
terminalstation

Optical fiber loop network

Fixed station
Broadcastingstation
Video
MUX

Service fortemporary use

Terminal station for terrestrial digital TV relay network
Terrestrial digital TV relay network (ATM)TV terminal link

Fig. 1. Application of portable wireless system for digital video transmission.

Antenna

Antenna

Receiving
radio unit

Transmitting
radio unit

Transmitter

Frequency
converter

Transmission
control unit

11/15
GHz
band

ReceiverFrequency
converter

Transmission
Modulator
signalprocessor

Reception
control unit

Demodulator

I/F

I/F
I/F

HDSDI

Received
signalprocessor

I/F

I/F
TripodNTSC, etc.
DVB-ASII/F

HDSDITripod
NTSC, etc.
DVB-ASI
DVB-ASI

DVB-ASI: HDTV codec board

Fig. 2. Configuration of portable wireless system for digital video transmission.

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Table 1. Main specifications.
Prototype

Commercial equipment

Frequency band

11-GHz band

11/15-GHz band

Transmission radio channel

48 channels

10 channels (11-GHz band), 6 channels (15-GHz band)

DVB-ASI, NTSC*1, HD-SDI (when HDTV codec boards are implemented)

User interfaces

Digital transmission: 64QAM (trellis 5/6), 32QAM (trellis 4/5), 16QAM (trellis 3/4), QPSK (no convolutional code)
Analog transmission: FM

Modulation
Error correction

RS(204,188)

Data rate (TS+RS)*2

66/60/53/45/40/30/25 Mbit/s*3

Symbol rate

13.35403 Mbit/s

Permissible spurious emission

50 µW

Permissible occupied bandwidth

Digital transmission: 15.5 MHz
Analog transmission: 17.0 MHz

Maximum frequency deviation (FM)Transmission power

8 MHzp-p
Digital transmission: 0.5 W/1.0 W/1.5 W
Analog transmission: 0.5 W

Digital transmission: 0.5 W/1.0 W
Analog transmission: 0.5 W

33 dBi (φ0.6 m)

11 GHz: 33 dBi (φ0.6 m), 36 dBi (φ0.9 m)
15 GHz: 35 dBi (φ0.6 m), 38 dBi (φ0.9 m)

Antenna gain
Volume, weight*4

28 liters, 30 kg*1 NTSC: Composite analog video signal standard for studio application, developed by the US National Television Systems Committee.
*2 TS: Transport Stream, RS: Reed Solomon*3 Data rate is converted from/into DVB-ASI rate (270 Mbit/s) by de-stuffing/stuffing.
*4 Total for transmission control unit, transmitting radio unit, reception control unit, and receiving radio unit

comparison with conventional portable wireless systems for analog video transmission that NTT developed in the past.

Fig. 3. Portable wireless system for digital video
transmission (prototype).

mercialized version are given in Table 1. To conformto the revised Radio Law Related Investigative Standards, we reduced the number of transmission channels and decreased the transmission power of thecommercialized version compared with the prototype. The appearance of the prototype system wedeveloped is shown in Fig. 3.
3. System features
The features of the system are described below in76

3.1 Countermeasures against incoming/outgoinginterference
Several fixed wireless links, such as the mobile
communications backhaul, use the same frequency
band as our system, especially the 11-GHz band.
Therefore, we must apply countermeasures against
outgoing and incoming interference to ensure that oursystem does not interfere with fixed wireless links
and to suppress interference from them.
To reduce outgoing interference, we implemented
functions for receiving and monitoring the radio
waves arriving at the transmitting radio unit. A spectrum analyzer monitors the incoming radio waves
from other fixed stations, enabling us to select themost suitable radio channel that does not harm otherfixed stations.
When the receiving radio unit is used in a severeinterference environment, we were concerned that thelow-noise amplifier might become saturated byincoming interference waves, degrading the linkquality. To handle this, we applied the two countermeasures shown in Fig. 4. An automatic gain control(AGC) permits the maximum received input to be–10 dBm and a group filter reduces the interference
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11-GHz band
(bandwidth: 1 GHz)

BPF111-GHz band

0
–10
–20
–30
–40
–50
–60
–70
–80

Desired Interferencewavewave

BPF2LNA
SWSW
BPF31010.51111.51212.5AGCBPF1
BPF4

BPF2

BPF3

BPF4

Attenuation characteristics of each filter(calculated values)

Desired Interference
wavewave
Maximum input
level is –10 dBm

SW: Switch
BPF: Band Pass Filter
LNA: Low Noise Amplifier
AGC: Automatic Gain Control

Control of BPF
selection

Fig. 4. Countermeasures against in-coming interference (prototype).

before it reaches the low-noise amplifier. The group filter comprises four bandpass filters and covers a total bandwidthof 1 GHz in the 11-GHz band. When theuser selects the radio channel, the filter
to be used is selected automatically.
As a result of these interference countermeasures, this system does not interfere with other fixed wireless links andprovides stable digital TV relay service
even under severe propagation conditions.

DVB-ASIDigitalmodulation
boardControl
board

clock
HD-SDI

Monitor/control bus

HDTV
codec
board

Digitalvoice(max. 4 ch)

3.2 Improved portability
PowerPower unit
Compared with the existing portablewireless system for analog video transmission, both the volume and the weightFig. 5. Implementation of HDTV codec board (transmission control unit).
have been decreased to improve portability. Previously, external codec unitswere necessary to transmit HDTV signals, but thesystem sends clock signals to set the encoding speed
new system incorporates a postcard-sized HDTV
and power to the board.
codec board (jointly developed by NHK and NTTCommunications). This reduces the number of pieces
3.3 Multiple interfacesof equipment to carry and shortens the system setup
The system has several interfaces besides DVBtime, enabling us to open a link quickly. The way thatASI*1 (a general-purpose serial interface for digital
the HDTV codec board is implemented in the transmission control unit is shown in Fig. 5. The parame*1 DVB-ASI: De facto standard for the asynchronous serial interface
ter settings for the codec board and the alarms issued
for digital video transmission established by the European DigitalVideo Broadcasting project. 270 Mbit/s.
from it pass through the monitor/control bus. ThisVol. 1 No. 5 Aug. 2003

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video transmission) to increase its applicability. As
described in section 3.2 by implementing the HDTV
codec board, the HD-SDI*2 interface can be provided.
Furthermore, because the system has interfaces foranalog video and analog audio (two channels), it canalso transmit existing analog video. During the transition period from analog to digital broadcasting, thissystem can be used in place of broken links and as atemporary link for analog relay, which will expand its
applicability.
3.4 Improved stability during deployment
In general, conventional portable wireless systems
used a friction-based method of setting the antenna’sangle of elevation on the tripod. In the new system,
we added a direct angle-of-elevation fixing mechanism consisting of a rotary joint and a locking screw.
This allows the antenna’s direction to be adjusted
finely and then fixed firmly, which improves the stability of the service. In addition, the tripod legs now
have metal plates with fixing bolts to anchor the tripod or secure its feet according to the conditions
where the tripod is set up.
4. Conclusion
This article presented the features of the portablewireless systems developed for digital video transmission. This system enables stable digital video
transmission under severe interference conditions byimplementing two interference countermeasures in
the receiving radio unit: RF automatic gain control
and automatic RF band pass filter selection. The volume and weight of this system have been decreased
to improve portability compared with portable wireless systems for analog video transmission that NTT
developed in the past.
In-house use of this system is planned for this year.
In the future, we will support a smooth commercial
introduction.

Tomotaka Yoshie
FWA Development Project, First Promotion
Project, NTT Access Network Service Systems
Laboratories.
He graduated from the department of electronic engineering, faculty of engineering, and completed his masters course at Tohoku University,Sendai, Miyagi, in 1993 and 1995 respectively
and joined NTT in 1995. He is mainly engaged inresearch, development, and the commercial
introduction of wireless access systems. Currently, he is engaged in the development of portablewireless systems for digital video transmission
and a WIPAS design tool. He is a member of theInstitute of Electronics, Information and Communication Engineers (IEICE) of Japan.

Hideyuki Maruyama
Senior Research Engineer, FWA Development
Project, First Promotion Project, NTT AccessNetwork Service Systems Laboratories.
He graduated from the department of electricalengineering, faculty of engineering, Niigata University, Niigata in 1985 and joined NTT in 1985.
He is mainly engaged in link design of fixedmicrowave systems and in the research, service
development, and commercial introduction ofsatellite communications systems. Currently, heis engaged in the development of portable wireless systems for digital video transmission and a
WIPAS design tool.

Toshio Saito
Senior Research Engineer, Supervisor, FWA
Development Project, First Promotion Project,NTT Access Network Service Systems Laboratories.
He graduated from the department of information engineering, faculty of engineering, Ibaraki
University in 1982. He completed his Masters
Course at Ibaraki University, Hitachi, Ibaraki in
1984 and joined NTT in 1984. He was mainly
engaged in the development of relay digital
microwave systems and their commercial introduction and business planning of long-distancecommunications. He is currently engaged in theresearch and development of a wireless IP accesssystem (WIPAS). He is a member of IEICE ofJapan.

*2 HD-SDI: High Definition Serial Data Interface: non-compressed
serial data transmission interface for HDTV video signal. Approximately 1.5 Gbit/s.

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