JPH036981A - Frequency division method in two-way catv system - Google Patents

Abstract

PURPOSE:To reduce mixed noise with a low frequency by increasing an incoming frequency band higher than an outgoing frequency band when the outgoing transmission line and the incoming transmission line are used in frequency division in a 2-way CATV system of one cable system. CONSTITUTION:When the outgoing frequency and the incoming frequency between a head end HE and a transmission reception installation TR are divided, the incoming frequency band is selected higher than the outgoing frequency band. For example, the incoming frequency band is set to 770MHz-900MHz, the outgoing frequency band is set similarly to 70MHz-450MHz. Thus, the incoming and outgoing frequency are divided and when the signal in two-way between the head end HE and the transmission reception installation (such as subscriber device) TR is sent, the signal transmission state of all the incoming band is improved. Thus, the effect of noise mixed in the head end is hardly produced.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a frequency division method in a two-way CATV system.

4. Prior Art As is well known, two-way CATV systems include a single cable system and a two cable system.

In the case of a single cable system, as is obvious, in one cable, the transmission path in the distribution direction (downward transmission path) and the transmission path in the opposite direction toward the head end (upward transmission path) are separated by frequency. In contrast, in the case of the two-strand cable system, separate cables are used for upstream and downstream directions.

A comparison of both these methods can be made as shown in the table below.

When considering the single-strand cable system and the double-strand cable system from this perspective, it seems that the two-strand cable system has many advantages over the single-strand cable system, but from an economic standpoint,
The strip cable method outperforms the double cable method.

Therefore, in a two-way CATV system, a single cable system is generally adopted based on the system's application target, economical structure, etc.

Figure 2 shows bidirectional CAT using the conventional single cable system.
In the V system, the headend HE and transmitting/receiving equipment (
(for example, subscriber equipment) shows an example of frequency division in the upstream and downstream directions across the TR.

In the case of such conventional examples, although the occupied frequency bandwidth differs depending on the system system, the frequency positional relationship is limited to the upstream frequency band (10 to 50 MHz).
z) is always set lower than the downstream frequency band (70 to 450 MHz).

rProblem to be solved by the invention J In the above-mentioned two-way CATV system, all the noise generated or mixed in from the transmission path, subscriber equipment, etc. flows to the head end via the upstream transmission path, and this As a result, the upstream signal deteriorates significantly.

These noises are collectively referred to as flow noise, but among them, mixed noise (jumping noise).

The lower frequencies tend to have higher levels.

Therefore, when the upstream band ranges from 10 to 50 MHz, as in the band division method illustrated in Fig. 2, i.e., the currently widely used sub-split method, the environmental noise around this frequency is extremely large. This makes it difficult to ensure good signal transmission conditions, and
The θ~50MHz band cannot be used for signal transmission.

In view of such technical problems, the present invention provides two-way CATV
The present invention aims to provide a frequency division method that can transmit upstream signals in a system with less flow noise.

``Means for Solving the Problems J'' In order to achieve the intended purpose, the frequency division method according to the present invention provides a downlink transmission path for distribution from the head end to the transmitting and receiving equipment in a bidirectional CATV system using a single cable system. , and an upstream transmission path in the opposite direction from the transmitting/receiving equipment to the head end.

When the frequency band is divided and used, the frequency band in the upstream direction is higher than the frequency band in the downstream direction.

In the case of the frequency division method according to the present invention, the predetermined bidirectional CA
In a TV system, since the frequency band in the upstream direction is set higher than the frequency band in the downstream direction, it is possible to reduce or avoid the influence of mixed noise at a low frequency in the upstream direction with a high frequency band. Good signal transmission conditions can be ensured in all bands.

Embodiment 1 The frequency division method in the bidirectional CATV system of the present invention will be explained with reference to an illustrated embodiment.

The two-way CATV system shown in FIG. 1 is based on the same single cable system as described in FIG.

In Figure 1, headend) IE and transmitting/receiving equipment TR
When dividing uplink and downlink frequencies over the range, the uplink frequency band is set higher than the downlink frequency band.

Specifically, as an example, the upstream frequency band is 770M.
Hz to 1300 MHz) and the downstream frequency band is set to 7014 Hz to 450 MHz as in the past.

In this way, when dividing the upstream and downstream frequencies and performing bidirectional signal transmission between the headend) IE and the transmitting/receiving value setting @ (for example, subscriber equipment) TR, for the reasons mentioned above, The signal transmission condition in the entire uplink band becomes good.

r Effects of the Invention J As explained above, the frequency division method in the bidirectional CATV system of the present invention makes the frequency band in the upstream direction higher than the frequency band in the downstream direction, so that the following effects can be obtained.

1) In the upstream band, it is not easily affected by noise that enters the head end, and therefore high quality communication can be achieved.

2) Since protective measures against noise contamination can be omitted or simplified, the economic efficiency of the system can be improved.

3) Since the downstream band may be the same as that of the conventional system, the existing specifications can be used as is.

4) The upstream band can be set much wider than before, and therefore sufficient channels can be secured even for full-scale CATV communication.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing an embodiment of the frequency division method according to the present invention, and FIG. 2 is an explanatory diagram schematically depicting a conventional frequency division method. HE・・・Head end TR・・・Transmission/reception equipment

Claims (1)

[Claims] In a two-way CATV system using a single cable system, when the downlink transmission path distributed from the head end to the transmitting/receiving equipment and the uplink transmission path in the opposite direction from the transmitting/receiving equipment to the head end are divided by frequency and used, the uplink A frequency division method in a two-way CATV system, characterized in that a frequency band in a direction is made higher than a frequency band in a downstream direction.