DIPOL Weekly Review

No. 32/2009 (Oct. 5, 2009)

The results of the photo contest "Engagingly about antennas".

The 8th edition of the contest organized by DIPOL has come to the end. As every year, the entries were adjudicated by well-known photographer from Krakow, Mr. Pawel Zechenter, who decided on the 1st and 2nd place winners. Another prize was awarded by our Technical Department.

I place:

Cycle: Window to the world

Wojciech Brozonowicz

II place:

Laundry...?
Jaroslaw Stefanski

Technical Department award:

Another dimension
of the antenna...
Darek Moszczynski

We have written about:

9-cable system - multiswitch installations. The most flexible multiswitch installations in multi-story buildings are based on 9-cable system (signals from two Quatro LNBs and terrestrial TV antenna). On each floor we employ the splitter providing signals to multiswitches. It allows to shape the network according to actual requirements - we may deploy practically unlimited number of outlets...
- archive DWR of Jan. 14, 2008

How to use wireless connectivity to develop the network at home or office. Internet access can be easily distributed among many users by wireless means. We present solutions based on TP-LINK devices...
- archive DWR of Sept. 8, 2008

How to use wireless connectivity to extend the network. Internet access is nowadays indispensable in any office, store, or hotel. It can be easily distributed among many users by wireless means. The diagram below shows an example when the connection is provided by...
- archive DWR of Jan. 19, 2009

Index of published issues

Other photos are available on the competition site. We congratulate the winners and thank all the contestants who have sent their works.

OFDM - a few words on WiFi - part 6.

The last of the described physical layers of the IEEE 802.11 standard is OFDM (Orthogonal Frequency-Division Multiplexing). Instead of transmitting one, large data stream on a single carrier (data sent in series, with rapid modulation), it is possible to divide the data into many sub-streams that modulate separate subcarrier waves at much slower rates. Modulation rate of each subcarrier is so low that the impact of the inter-symbol interference is noticeable only in a small, initial fragment of the guard interval of the modulation.

In a classical system of parallel transmission (FDM) the total available bandwidth is divided into N parts, separated from each other, one for each sub-channel. Each of them is a separate modulated signal and N sub-channels are multiplexed in the frequency domain. Isolation between bands (spectra) of individual sub-channels (separation in frequency domain) is an effective way to avoid inter-channel interference. Unfortunately, it causes inefficient use of available bandwidth. Therefore, there have been developed systems, in which the bands of individual channels do overlap. To use the overlapping of the bands it is necessary to reduce the crosstalk to acceptable levels, i.e to achieve orthogonality between the carriers. Comparison of the spectrum of the classical parallel transmission system and OFDM system has been illustrated in the following figure.

Comparison of the spectra of classical parallel transmission system (a) and OFDM system (b)

There is a possibility of such a choice of the carrier frequencies that the bands of individual carrier signals overlap, yet they can be received without interference. This situation occurs when the carriers are mathematically orthogonal, i.e. when the distance between them is an integer multiple of 1/T. T is the orthogonality interval, being the part of the guard interval in which the carrier signals are mutually orthogonal. The sub-carrier spacing of 1/T makes them orthogonal over each symbol period. The following figure shows the spectra of a single-carrier signal and of several mutually orthogonal subcarriers.

The spectra of a single-carrier signal and of several mutually orthogonal subcarriers

It should be noted that in places where spectral density of each carrier reaches its maximum, the density of other carriers has values equal to 0. Therefore, demodulating the OFDM signal exactly in those places, inter-channel interference can be completely eliminated.

OFDM signal is the sum of subcarriers modulated with PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation). Below there is a block diagram showing the principle of operation of OFDM modulator:

Block diagram explaining the operation of OFDM modulator

Example form of OFMD signal in time domain:

An OFMD signal in time domain

In conclusion, the data stream in OFDM systems is divided into many separate elements, which modulate orthogonal subcarriers. The orthogonality eliminates inter-channel interference. The data rate on each subcarrier is a small fraction of the transmission speed of the device. The duration of any bit modulating the subcarrier is many times longer than the bit duration of the original message and much more longer than the dispersion of the transmission delay caused by multipath signal propagation. The main advantage of OFDM is its ability to cope with such conditions, e.g. with narrowband interference and frequency-selective fading due to multiple reflections - only a part of the transmitted data stream degrades. In order to achieve a compromise between high modulation efficiency (expressed in the number of bits/Hz) and resistance to interference, the subcarriers are modulated with various schemes, depending on the conditions prevailing in the channel. The devices have mechanisms of signal analysis and choose the appropriate modulation.

DVB receivers for reception of free TVP programs (Polish public TV).

Since September 15, 2009, TVP has launched its own digital satellite platform. The programs are broadcast from the 59th transponder of ASTRA 1KR (19.2E). The current program offer includes the following open TV channels: TVP1, TVP2, TVP Info, TVP HD, TVP Sport, TVP Puls (TV), and the following radio channels: Parliament, PR 1, PR 2, PR 3, PR Euro and PR for Foreigners. In the near future it will be expanded by TVP Seriale (Series) oraz TVP Parliament.

Our company is getting increasing numbers of inquiries relating to the modification of existing antenna systems to have the capability of receiving the above package. Assuming that the installation has only one LNB for Hotbird satellite, there are two options:

Use of another single LNB (e.g. A9825) placed in parallel the existing one on additional LNB mount (A9891 or A9892, depending on the arm). The LNBs have to be conneted to DiseqC switch R85250.
Replacement of the single LNB with monoblock LNB A98255 with built-in DiseqC switch.

For proper reception of both satellites the dish should have at least 80 cm diameter.

In the case of proper antenna installation another issue is appropriate DVB-S/S2 receiver. The signals from the TVP transponder are compressed in the MPEG-4 standard. The DVB receivers that support only the MPEG-2 compression will not receive the desired channels. All HD receivers currently offered by DIPOL support MPEG-4 compression.

Since December the TVP platform will be expanded by pay channels encoded in the NDS Videogurad system. For the moment, on the market there are no receivers certified by TVP. Our company is monitoring the situation and any changes will be reflected in the offer and in DIPOL Weekly Review.

Extensive monitoring systems based on optical fibers.

Already during the design of an extensive monitoring system there is the problem of integration of the images from all the cameras in a single point of management. The problem arises in installations based on coaxial cables already with lengths of 100 m or so, and is visible as loss of color, lower contrast and sharpness. It can be solved by using fiber optic systems. The example of the dedicated series of fiber optic devices is ULTIMODE. With advanced WDM technology used in ULTIMODE video converters the images from CCTV cameras can be transmitted over distances up to 20 km, using only single optic fiber. The images are sent in real time without any loss of quality. Such large distances are possible due to use of video converters based on laser diodes with Fabry-Perot resonators and optical fibers with very low attenuation:

for 850 nm: < 1.5 dB/km
for 1310 nm: < 0.4 dB/km
for 1550 nm: < 0.2 dB/km

An example of such extensive monitoring system is given below:

Example of installation using the ULTIMODE series of video converters

1 - Monitoring center

2 - Main node

3 - School monitoring system

4 - City monitoring system

ULTIMODE video converters

ULTIMAX mini DVRs - operation in the network.

One of main advantages of ULTIMAX-104 M71040 and ULTIMAX-204 M72040 DVRs is network operation. Thanks to H.264 compression the video data can be effectively transmitted via networks with narrower bandwidth than in the case of other DVRs. Additionally, the band can be independently set for each channel. Simultaneous remote access to the DVR is limited by the bandwidth of the link. Monitoring of several DVRs can be executed via Internet Explorer or client program ("Net Video Application") which is a free supplement to the DVRs. In addition to these advantages, the recorder possesses one more important feature: the ability to define two different streams for each channel separately - the one recorded in the local network and the second sent to the "world" via the Internet. This function is extremely important when the speed of Internet access is comparatively low. Lower quality of images transmitted through the network will provide greater smoothness of the video, while the higher recording parameters allow for better identification and analysis of the archival data.

ULTIMAX 104 and 204 DVRs connected to the Internet

Megapixel video surveillance system with ACTi cameras in Krakow.

Plac Nowy (New Square) in Krakow is a place frequented by tourists from around the world and a very fashionable place for socializing. The popularity of this site sometimes has its disadvantages, including frequent violations of the law. With this in mind, the management company of the area has decided to mount CCTV cameras. Installation works were carried out by "SCAZI" company from Krakow.

The system employs 5 megapixel cameras ACTI ACM 5611 K1512 and two 1.3 Mpx dome cameras ACTI ACM 7411 K1313

Due to specific conditions, the video data from some cameras are transmitted wirelessly in 5 GHz band. The system will contribute to improving security in the area. It has already gained the recognition of the city police. In the future some cameras will be installed on special poles around the rotunda, allowing to realize the full potential of megapixel cameras.

Screenshots from the system monitoring Plac Nowy in Kazimierz district in Krakow

Training of ACTi IP cameras and CCTV systems design.

The latest CCTV training was focused on configuration of IP cameras and systems design. The course was attended by the representative of ACTi - Ms. Anna Tsai, who at the end of the short course tested the knowledge of the participants. We thank everybody for their attendance and welcome to another trainings and courses.

ACTi training conducted by Mr. M. Wlodarczyk and Ms. A. Tsai

Great sensitivity and power - SparkLAN WMIA-123AG 802.11a/b/g.

Wireless network card SparkLAN WMIA-123AG 802.11a/b/g N2717 can operate in all standards - IEEE802.11a/b/g. It allows to connect a computer to the local network (LAN). The mini-PCI SparkLAN WMIA-123AG card is suitable for mobile computers and RouterBoard cards run by Mikrotik system.

Distinguishing features:

support for 802.11a, 802.11b, and 802.11g standards,
support for Super AG (transmission speed up to 108 Mbit/s),
mini-PCI type III B interface,
support for 64/128/152 WEP; AES,
main application: wireless module for RouterBoard main board (Mikrotik OS).

Wireless network card SparkLAN WMIA-123AG 802.11a/b/g
N2717

The SparkLAN WMIA-123AG card is the optimum wireless module for the following RouterBoard main boards:

RouterBoard 411 N24113;
RouterBoard 411A N24114;
RouterBoard 433 N24334.

Stylish and modern Monako mounts.

Monako series is a wide range of brackets for mounting LCD monitors and plasma TVs on a wall or ceiling. Application of the mounts significantly increases the comfort and space in an apartment or room. Monako brackets solve the problem of mounting a TV, projector or monitor on the ceiling or wall and allow to adjust its position to the needs of the user/s.
Each kit contains a full set of screws, nuts, washers, and spacers for easy installation of the mount.