Carrier aggregation wireless network system and base station, wireless communication device, and synchronization method thereof

A carrier aggregation wireless network system and a base station (BS), a wireless communication device, and a synchronization method thereof are disclosed. The wireless communication device receives a wireless signal from the BS. The wireless signal includes a primary cell (pcell) and a secondary cell (scell). A subframe of the scell includes a first OFDM symbol and a second OFDM symbol. The first OFDM symbol includes an extended primary synchronization signal (PSS). The second OFDM symbol includes a PSS. The scell includes a secondary synchronization signal (SSS). The wireless communication device acquires synchronization according to the extended PSS and/or the PSS. In addition, the wireless communication device may also acquire synchronization according to a cell ID, the PSS, and the SSS.

TECHNICAL FIELD

The technical field relates to a synchronization technique in a carrier aggregation wireless network system, and more particularly, to a carrier aggregation wireless network system and a base station, a wireless communication device, and a synchronization method thereof.

BACKGROUND

In order to set up and provide a fast and convenient information transmission environment, people have been constantly developing and upgrading existing wireless networks (for example, mobile communication networks). In an orthogonal frequency-division multiplexing (OFDM) long term evolution (LTE) system, a carrier resource of no more than 20M is allocated to each user equipment (UE, also referred to as user device). However, to achieve a greater transmission bandwidth, 2 or more component carriers (CC) are aggregated. For example, carrier aggregation (including contiguous carrier aggregation and interband and intraband non-contiguous carrier aggregation) is supported in a LTE-advanced system to achieve a maximum aggregatable bandwidth of up to 100 MHz. Thus, 1-5 CCs may be allocated to a specific UE, and accordingly, resources used or collected by the UE may be distributed on these 1-5 CCs.

In a wireless network system (for example, a mobile communication network system), a base station (BS) is usually served as the access point of many wireless communication devices. Herein a wireless communication device may be a mobile station (MS, for example, a cell phone) or a user device (for example, a notebook computer). However, the MS may also be a user device and vice versa. A wireless communication device may be an immobile device (for example, a personal computer (PC)) or a mobile device (for example, a cell phone, a tablet PC, or any other mobile communication device).

Because each macro BS has a very large coverage area (also referred to as a macro coverage area) and supports a large number of wireless communication devices within its coverage area, each macro BS carries a heavy communication load. Besides, a macro BS is difficult to deploy due to environmental awareness and opposition. Additionally, because communication-starved spots may exist inside a building because of the deployed position of a BS or the shield of buildings or other objects, indoor communication quality may not be very satisfactory. Thus, the deployment of local or sub BSs (for example, pico BSs, femto BSs, and home BSs) has become a preferred solution for improving indoor communication performance.

A sub BS offers a low power, a great bandwidth, and a small sub coverage area therefore can improve the communication performance of any wireless communication device within its coverage area. However, because the coverage area of a macro BS and the coverage area of a sub BS often overlap each other, data transmitted within these two areas may interfere with each other. Moreover, the transmission performance of a macro BS may be affected by such interference or any issue regarding transmission resource allocation.

SUMMARY

The disclosure provides a synchronization method of a carrier aggregation wireless network system. The wireless network system includes a first base station (BS), a second BS, and a wireless communication device. A part of the coverage area of the first BS overlaps a part of the coverage area of the second BS. The synchronization method includes following steps. A first wireless signal is transmitted by the first BS. The first wireless signal includes a first subframe. The first subframe includes a first orthogonal frequency-division multiplexing (OFDM) symbol. The first OFDM symbol includes an extended primary synchronization signal (PSS). The extended PSS is sequentially a first periodic extension, a low-frequency part, a DC carrier, a high-frequency part, and a second periodic extension in order of increasing frequency on the spectrum. The DC carrier is a subcarrier located at the center of the baseband. The first periodic extension and the high-frequency part carry the same data. The second periodic extension and the low-frequency part carry the same data. A second wireless signal is transmitted by the second BS. The second wireless signal includes a second subframe. The second subframe includes a plurality of OFDM symbols. One of the OFDM symbols of the second subframe that is corresponding to the first OFDM symbol includes a PSS. The PSS is sequentially the low-frequency part, the DC carrier, and the high-frequency part in order of increasing frequency on the spectrum. The wireless communication device acquires synchronization according to the extended PSS.

The disclosure provides a carrier aggregation wireless network system including a first BS, a second BS, and a wireless communication device. The first BS transmits a first wireless signal. The first wireless signal includes a first subframe. The first subframe includes a first OFDM symbol. The first OFDM symbol includes an extended PSS. The extended PSS is sequentially a first periodic extension, a low-frequency part, a DC carrier, a high-frequency part, and a second periodic extension in order of increasing frequency on the spectrum. The DC carrier is a subcarrier located at the center of the baseband. The first periodic extension and the high-frequency part carry the same data. The second periodic extension and the low-frequency part carry the same data. The second BS transmits a second wireless signal. The second wireless signal includes a second subframe. The second subframe includes a plurality of OFDM symbols. One of the OFDM symbols of the second subframe that is corresponding to the first OFDM symbol includes a PSS. The PSS is sequentially the low-frequency part, the DC carrier, and the high-frequency part in order of increasing frequency on the spectrum. The wireless communication device acquires synchronization according to the extended PSS.

The disclosure provides a BS of a carrier aggregation wireless network system. The BS transmits a wireless signal. The wireless signal includes a subframe. The subframe includes a first OFDM symbol. The first OFDM symbol includes an extended PSS. The extended PSS is sequentially a first periodic extension, a low-frequency part, a DC carrier, a high-frequency part, and a second periodic extension in order of increasing frequency on the spectrum. The DC carrier is a subcarrier located at the center of the baseband. The first periodic extension and the high-frequency part carry the same data. The second periodic extension and the low-frequency part carry the same data.

The disclosure provides a wireless communication device of a carrier aggregation wireless network system. The wireless communication device receives a wireless signal. The wireless signal includes a subframe. The subframe includes a first OFDM symbol. The first OFDM symbol includes an extended PSS. The extended PSS is sequentially a first periodic extension, a low-frequency part, a DC carrier, a high-frequency part, and a second periodic extension in order of increasing frequency on the spectrum. The DC carrier is a subcarrier located at the center of the baseband. The first periodic extension and the high-frequency part carry the same data. The second periodic extension and the low-frequency part carry the same data. The wireless communication device acquires synchronization according to the extended PSS.

The disclosure provides a synchronization method of a carrier aggregation wireless network system. The wireless network system includes a first BS, a second BS, and a wireless communication device. A part of the coverage area of the first BS overlaps a part of the coverage area of the second BS. The synchronization method includes following steps. A first wireless signal is transmitted by the first BS. The first wireless signal includes a first subframe. The first subframe includes a first OFDM symbol and a second OFDM symbol. The first OFDM symbol includes a PSS, and the second OFDM symbol also includes the PSS. A second wireless signal is transmitted by the second BS. The second wireless signal includes a second subframe. The second subframe includes a plurality of OFDM symbols. One of the OFDM symbols of the second subframe that is corresponding to the first OFDM symbol includes the PSS. The wireless communication device acquires synchronization according to the PSS of the second OFDM symbol.

The disclosure provides a carrier aggregation wireless network system including a first BS, a second BS, and a wireless communication device. The first BS transmits a first wireless signal. The first wireless signal includes a first subframe. The first subframe includes a first OFDM symbol and a second OFDM symbol. The first OFDM symbol includes a PSS, and the second OFDM symbol also includes the PSS. The second BS transmits a second wireless signal. The second wireless signal includes a second subframe. The second subframe includes a plurality of OFDM symbols. One of the OFDM symbols of the second subframe that is corresponding to the first OFDM symbol includes the PSS. The wireless communication device acquires synchronization according to the PSS of the second OFDM symbol.

The disclosure provides a BS of a carrier aggregation wireless network system. The BS transmits a wireless signal. The wireless signal includes a subframe. The subframe includes a first OFDM symbol and a second OFDM symbol. The first OFDM symbol includes a PSS, and the second OFDM symbol also includes the PSS.

The disclosure provides a wireless communication device of a carrier aggregation wireless network system. The wireless communication device receives a wireless signal. The wireless signal includes a subframe. The subframe includes a first OFDM symbol and a second OFDM symbol. The first OFDM symbol includes a PSS, and the second OFDM symbol also includes the PSS. The wireless communication device acquires synchronization according to the PSS of the second OFDM symbol.

The disclosure provides a synchronization method of a carrier aggregation wireless network system. The wireless network system includes a BS and a wireless communication device. The synchronization method includes following steps. A wireless signal is transmitted by the BS. The wireless signal includes a first cell having a first component carrier (CC) as its frequency band and a second cell having a second CC as its frequency band. The second cell includes a PSS and a secondary synchronization signal (SSS). A cell ID of the second cell is obtained by the wireless communication device according to the first cell. The wireless communication device is synchronized according to the cell ID and the PSS and the SSS of the second cell.

The disclosure provides a carrier aggregation wireless network system including a BS and a wireless communication device. The BS transmits a wireless signal. The wireless signal includes a first cell having a first CC as its frequency band and a second cell having a second CC as its frequency band. The second cell includes a PSS and a SSS. The wireless communication device obtains a cell ID of the second cell according to the first cell. The wireless communication device acquires synchronization according to the cell ID and the PSS and the SSS of the second cell.

The disclosure provides a wireless communication device of a carrier aggregation wireless network system. The wireless communication device receives a wireless signal. The wireless signal includes a first cell having a first CC as its frequency band and a second cell having a second CC as its frequency band. The second cell includes a PSS and a SSS. The wireless communication device obtains a cell ID of the second cell according to the first cell. The wireless communication device acquires synchronization according to the cell ID and the PSS and the SSS of the second cell.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

Reference will now be made in detail to some embodiments of the disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. These embodiments are described below in order to explain the disclosure but are not intended to limit the scope of the disclosure. To be specific, these embodiments are only examples of the systems and methods claimed by the disclosure.

FIG. 1is a diagram of a carrier aggregation wireless network system according to an embodiment of the disclosure. The system is illustrated inFIG. 1for the convenience of description but not intended to limit the scope of the disclosure. Referring toFIG. 1, the wireless network system100includes a first base station (BS)110, a second BS120, and wireless communication devices130and140, etc. The first BS110may be a sub BS, and which may be a pico BS, a femto BS, a home BS, or any other type of BS. The second BS120may be a macro BS. Part of the coverage area of the first BS110overlaps part of the coverage area of the second BS120. Herein “part of a coverage area” may refer to the entire coverage area or only a part of the coverage area. The wireless communication devices130and140are user equipments (UEs), such as cell phones, tablet computers, or notebook computers. In the present embodiment, the wireless network system100is a heterogeneous network system, the first BS110is a pico BS of a sub BS, and the second BS120is a macro BS. However, the disclosure is not limited thereto, and any other combination is within the scope of the disclosure. For example, the first BS110and the second BS120may both be macro BSs with overlapping coverage areas.

The first BS110emits or transmits a first wireless signal. The first wireless signal is a carrier aggregation wireless signal and at least includes a first component carrier (CC) and a second CC. Herein the frequency at the center of the baseband of the first CC is f1, and the frequency at the center of the baseband of the second CC is f2. In the present embodiment, the resources used by the wireless communication device130include the first CC and the second CC. Thus, when the first BS110serves as the access point of the wireless communication device130, the first wireless signal includes a first cell132(for example, a primary cell (pcell)) having the first CC as its frequency band and a second cell134(for example, a secondary cell (scell)) having the second CC as its frequency band. The first cell132includes a physical downlink control channel (PDCCH)136. The PDCCH136contains information related to the second cell134such that the wireless communication device130can read data from the second cell134accordingly. As mentioned above, the first cell132is a pcell and the second cell134is a scell. However, the disclosure is not limited thereto, and any other cell is also within the scope of the disclosure. For example, the second cell134may be a cell other than a scell.

Similarly, the second BS120emits or transmits a second wireless signal. The second wireless signal is also a carrier aggregation wireless signal and also includes at least two CCs having the frequencies f1and f2at the centers of the basebands thereof. In the present embodiment, the resources used by the wireless communication device140include these two CCs having the frequencies f1and f2at the centers of the basebands thereof. However, when the second BS120serves as the access point of the wireless communication device140, the CC having the frequency f2at the center of the baseband thereof carries a pcell142, while the CC having the frequency f1at the center of the baseband thereof carries a scell144. Similarly, the pcell142includes a PDCCH146, and the PDCCH146contains information related to the scell144such that the wireless communication device140can read data from the scell144accordingly.

As shown inFIG. 1, the second BS120uses the regular emission power when it emits the CC having the frequency f2at the center of the baseband and offers a coverage area126. However, to improve the transmission performance, the second BS120uses a lower emission power when it emits the CC having the frequency f1at the center of the baseband and offers a coverage area128. Thus, the coverage area128is much smaller than the coverage area126. In the present embodiment, the first BS110is a sub BS with a relatively small emission power. Following expression is satisfied within the coverage area112illustrated inFIG. 1:
P1st>P2nd(1)

Following expression is satisfied within the coverage area114illustrated inFIG. 1:
P1st>P2nd−Poffset(2)

In foregoing expressions, P1stis the power of the wireless signal received from the first BS110, P2ndP is the power of the wireless signal received from the second BS120, and Poffsetis a predetermined power compensation value. The area inside the coverage area114but outside the coverage area112is referred to as a range extension (RE)116of the first BS110. InFIG. 1, the overlapping between the coverage areas of the first BS110and the second BS120is not intended to limit the disclosure, and any other whole or partial overlapping between coverage areas is within the scope of the disclosure.

The wireless communication device140is located within the coverage area128. Thus, when the second BS120serves as the access point of the wireless communication device140, regarding a wireless signal of a CC having the frequency f2at the center of the baseband, the power of the wireless signal received from the second BS120is much greater than the power of the wireless signal received from the first BS110, and the wireless communication device140can easily acquire synchronization of the pcell142with the second BS120. Similarly, the wireless communication device140can easily acquire synchronization of the scell144with the second BS120.

The wireless communication device130is located within the coverage area112. Thus, when the first BS110serves as the access point of the wireless communication device130, regarding a wireless signal of a CC having the frequency f1at the center of the baseband, the power of the wireless signal received from the first BS110is much greater than the power of the wireless signal received from the second BS120, and the wireless communication device130can easily acquire synchronization of the pcell132with the first BS110. In addition, regarding a wireless signal of the CC having the frequency f2at the center of the baseband, because the power of the wireless signal received from the first BS110is greater than the power of the wireless signal received from the second BS120within the coverage area112, the wireless communication device130can easily acquire synchronization of the scell134with the first BS110. However, if the wireless communication device130is located within the RE116or moves from the coverage area112to the RE116, because the second BS120uses relatively low emission power when it emits the CC having the frequency f1at the center of the baseband, to the wireless signal of the CC having the frequency f1at the center of the baseband, the power of the wireless signal received from the first BS110is still greater than the power of the wireless signal received from the second BS120. Thus, the wireless communication device130can still acquire synchronization of the pcell132with the first BS110. However, within the RE116, regarding a wireless signal of the CC having the frequency f2at the center of the baseband, the power of the wireless signal received from the first BS110is smaller than the power of the wireless signal received from the second BS120, and due to interference or the distance between the CC having the frequency f1at the center of the baseband and the CC having the frequency f2at the center of the baseband, the wireless communication device130cannot acquire synchronization of the scell134with the first BS110.

FIG. 2Ais a resource allocation diagram of a carrier aggregation wireless network system working in a frequency-division duplexing (FDD) mode according to an embodiment of the disclosure. The resource allocation is illustrated inFIG. 2Afor the convenience of description but not intended to limit the scope of the disclosure. Referring to bothFIG. 1andFIG. 2A, the first BS110transmits a first wireless signal. As described above, the first wireless signal includes a second CC having a frequency f2at the center of the baseband. The second CC carries a scell134. The scell134includes a first subframe210. The first subframe210includes a plurality of (for example, 14) orthogonal frequency-division multiplexing (OFDM) symbols. The OFDM symbols include a first OFDM symbol212(for example, the 7thOFDM symbol is the first OFDM symbol212). The first OFDM symbol212includes an extended primary synchronization signal (PSS)216. Another OFDM symbol (for example, the 6thOFDM symbol) of the first subframe210includes a secondary synchronization signal (SSS)214.

The second BS120transmits a second wireless signal. The second wireless signal includes a CC having the frequency f2at the center of the baseband. The CC carries a pcell142. The pcell142includes a second subframe220. The second subframe220includes a plurality of (for example, 14) OFDM symbols. One of the OFDM symbols that is corresponding to the first OFDM symbol212includes a PSS228. Since the first OFDM symbol212is the 7thOFDM symbol, the OFDM symbol corresponding to the first OFDM symbol212is also the 7thOFDM symbol222. Namely, the 7thOFDM symbol222includes the PSS228. Another OFDM symbol (for example, the 6thOFDM symbol) of the second subframe220also includes the SSS214.

FIG. 2Bis a resource allocation diagram of a carrier aggregation wireless network system working in a time-division duplexing (TDD) mode according to an embodiment of the disclosure. The resource allocation is illustrated inFIG. 2Bfor the convenience of description but not intended to limit the scope of the disclosure. Please refer to bothFIG. 1andFIG. 2B. The embodiments illustrated inFIG. 2AandFIG. 2Bshow the difference between operations in the FDD mode and the TDD mode, and similar or same aspects in the two embodiments will not be described herein. In general, the first BS110transmits a first wireless signal. The first wireless signal includes a first subframe250. The first subframe250includes a first OFDM symbol252(for example, the 3rdOFDM symbol is the first OFDM symbol252). The first OFDM symbol252includes an extended PSS256. The second BS120transmits a second wireless signal. The second wireless signal includes a second subframe260. The second subframe260includes a plurality of OFDM symbols. One of the OFDM symbols of the second subframe260that is corresponding to the first OFDM symbol252includes a PSS268. Since the first OFDM symbol252is the 3rdOFDM symbol, the OFDM symbol corresponding to the first OFDM symbol252is the 3rdOFDM symbol262. Namely, the 3rdOFDM symbol262includes the PSS268. In addition, in the present embodiment, the wireless network system works in the TDD mode, and a SSS254is configured in the last OFDM symbol of a subframe before the first subframe250and the second subframe260.

FIG. 3is a spectrum diagram of an extended primary synchronization signal (PSS) and a PSS according to an embodiment of the disclosure. The spectrum is illustrated inFIG. 3for the convenience of description but not intended to limit the scope of the disclosure. Referring toFIG. 3, the extended PSS is sequentially a first periodic extension312, a low-frequency part314, a DC carrier, a high-frequency part316, and a second periodic extension318in order of increasing frequency on the spectrum. The DC carrier is a subcarrier located at the center of the baseband, the first periodic extension312and the high-frequency part316carry the same data, and the second periodic extension318and the low-frequency part314carry the same data. The PSS is sequentially the low-frequency part314, the DC carrier, and the high-frequency part316in order of increasing frequency on the spectrum.

Here the 3GPP Rel-10 standard will be taken as an example, and a PSS may be generated by using a Zadoff-Chu sequence du(n) on a spectrum, as shown below:

In foregoing expression (3), u is a Zadoff-Chu root index, and the value thereof is shown in following table:

In foregoing table, NID(2)is an individual ID (which has 0, 1, or 2 as its value), and which is determined by the cell ID of the cell corresponding to the signal. The cell ID is equal to the cell group ID NID(1)times3and plus the individual ID NID(2). The cell group ID NID(1)has a value of any one among 0-167. The low-frequency part314and the high-frequency part316in the PSS have totally 6 resource blocks (RBs), and each RB has 12 subcarriers. Namely, there are totally 72 subcarriers. By removing the 5 blank (nil) low-frequency subcarriers from the left side, the 5 blank (nil) high-frequency subcarriers from the right side, and the DC carrier in the middle, a signal generated by using the Zadoff-Chu sequence is exactly mapped to the 62 subcarriers at the middle of the PSS.

The first periodic extension312, the low-frequency part314, the high-frequency part316, and the second periodic extension318in the extended PSS have totally 12 RBs. Because the extended PSS has a signal sequence longer than general standard sequence, synchronization can be easily acquired by using the extended PSS even when interference exists. Besides, because the low-frequency part314and the high-frequency part316in the extended PSS are exactly the same as the low-frequency part314and the high-frequency part316in the PSS, the first periodic extension312and the high-frequency part316carry the same data, and the second periodic extension318and the low-frequency part314carry the same data, the technique in the disclosure is compatible to any general standard.

When the wireless communication device130is located within the RE116, it receives both the first wireless signal and the second wireless signal. Regarding a wireless signal of the CC having the frequency f2at the center of the baseband, the power of the wireless signal received from the first BS110is smaller than the power of the wireless signal received from the second BS120. Thus, the wireless communication device130in seriously interfered and accordingly is unable to acquire synchronization of the scell134with the first BS110. However, the wireless communication device130generates a synchronization preamble according to the extended PSS and performs a correlation operation on the synchronization preamble and the received wireless signal, so that the wireless communication device130can easily acquire synchronization of the scell134with the first BS110by using the result of the correlation operation. The technique in the disclosure is not limited to an application within the RE116and may also be applied to other areas without departing the scope of the disclosure.

FIG. 4Ais a resource allocation diagram of a carrier aggregation wireless network system working in a FDD mode according to another embodiment of the disclosure. The resource allocation is illustrated inFIG. 4Afor the convenience of description but not intended to limit the scope of the disclosure. Referring to both FIG.1andFIG. 4A, as described above, the first BS110transmits a first wireless signal. The first wireless signal includes a second CC having the frequency f2at the center of the baseband. The second CC carries a scell134. The scell134includes a first subframe410. The first subframe410includes a plurality of (for example, 14) OFDM symbols. The OFDM symbols include a first OFDM symbol412and a second OFDM symbol414. For example, the 5thOFDM symbol is the second OFDM symbol414, and the 7thOFDM symbol is the first OFDM symbol412. The first OFDM symbol412includes a PSS228, and the second OFDM symbol414also includes the PSS228. The first subframe410further includes another OFDM symbol (for example, the 6thOFDM symbol). This another OFDM symbol includes a SSS214.

The second BS120transmits a second wireless signal. The second wireless signal includes a CC having the frequency12at the center of the baseband. The CC carries a pcell142. The pcell142includes a second subframe420. The second subframe420includes a plurality of (for example, 14) OFDM symbols. One of the OFDM symbols that is corresponding to the first OFDM symbol412includes the PSS228. Because the first OFDM symbol412is the 7thOFDM symbol, the OFDM symbol corresponding to the first OFDM symbol412is also the 7thOFDM symbol422. Namely, the 7thOFDM symbol422includes the PSS228. Another OFDM symbol (for example, the 6thOFDM symbol) of the second subframe420also includes the SSS214.

FIG. 4Bis a resource allocation diagram of a carrier aggregation wireless network system working in a TDD mode according to another embodiment of the disclosure. The resource allocation is illustrated inFIG. 4Bfor the convenience of description but not intended to limit the scope of the disclosure. Please Refer to bothFIG. 1andFIG. 4B. The embodiments illustrated inFIG. 4AandFIG. 4Bshow the difference between operations in the FDD mode and the TDD mode, and similar or same aspects of the two embodiments will not be described herein. In general, the first BS110transmits a first wireless signal. The first wireless signal includes a first subframe450. The first subframe450includes a first OFDM symbol452and a second OFDM symbol454. For example, the 2ndOFDM symbol is the second OFDM symbol454, and the 3rdOFDM symbol is the first OFDM symbol452. The first OFDM symbol452includes a PSS268, and the second OFDM symbol454also includes the PSS268. The second BS120transmits a second wireless signal. The second wireless signal includes a second subframe460. The second subframe460includes a plurality of OFDM symbols. One of the OFDM symbols of the second subframe460that is corresponding to the first OFDM symbol452includes the PSS268. Because the first OFDM symbol452is the 3rdOFDM symbol, the OFDM symbol corresponding to the first OFDM symbol452is also the 3rdOFDM symbol462. Namely, the 3rdOFDM symbol462includes the PSS268. In addition, in the present embodiment, the wireless network system works in the TDD mode, and the SSS254is configured in the last OFDM symbol of the subframe before the first subframe450and the second subframe460.

The wireless communication device130is located within a RE116, and which receives both the first and the second wireless signal. Regarding a wireless signal of the CC having the frequency f2at the center of the baseband, the power of the wireless signal received from the first BS110is smaller than the power of the wireless signal received from the second BS120. If the wireless communication device130acquires synchronization of the scell134by using only the PSS of the first OFDM symbol, since the OFDM symbol in the wireless signal emitted by the second BS120that is corresponding to the first OFDM symbol also includes the PSS, the wireless communication device130is seriously interfered. In this case, the wireless communication device130acquires synchronization of the scell134with the first BS110by using the PSS of the second OFDM symbol, so that aforementioned interference problem can be easily resolved. The technique in the disclosure is not limited to an application within the RE116and may also be applied to other areas without departing the scope of the disclosure.

Referring toFIG. 4Aagain. One of the OFDM symbols of the second subframe420that is corresponding to the second OFDM symbol414includes a frequency band carrying blank data. Because the second OFDM symbol414is the 5thOFDM symbol, the OFDM symbol corresponding to the second OFDM symbol414is also a 5thOFDM symbol424. To be specific, data on the frequency band of the spectrum of the OFDM symbol424that is the same as the frequency band of the PSS of the second OFDM symbol414is nil. Namely, the second BS120does not emit data or uses a relatively low emission power on the same frequency band at the same time point. Thus, the wireless communication device130can acquire synchronization of the scell134by using the PSS228of the second OFDM symbol.

Referring toFIG. 4Bagain, one of the OFDM symbols of the second subframe460that is corresponding to the second OFDM symbol454includes a frequency band carrying blank data. Because the second OFDM symbol454is the 2ndOFDM symbol, the OFDM symbol corresponding to the second OFDM symbol454is also a 2ndOFDM symbol464. To be specific, data on the frequency band of the spectrum of the OFDM symbol464that is the same as the frequency band of the PSS of the second OFDM symbol454is nil. Namely, the second BS120does not emit data or uses a relatively low emission power on the same frequency band at the same time. Thus, the wireless communication device130can acquire synchronization of the scell134by using the PSS268of the second OFDM symbol.

In the embodiments illustrated inFIG. 4AandFIG. 4B, one of the OFDM symbols of the second subframe that is corresponding to the second OFDM symbol includes a blank frequency band. However, the disclosure is not limited thereto, and this blank frequency band may also be allocated as usable resource for downlink transmitting actual data.

The embodiment illustrated in2A andFIG. 4Aor inFIG. 2BandFIG. 4Bis technically independent. However, the disclosure is not limited thereto. In an actual application, the technique illustrated inFIG. 2AandFIG. 4Aand the technique illustrated inFIG. 2BandFIG. 4Bmay coexist in a carrier aggregation wireless network system to ensure the acquisition of synchronization.

FIG. 5is a block diagram illustrating synchronization-related functions of a wireless communication device of a carrier aggregation wireless network system according to yet another embodiment of the disclosure. The device is illustrated inFIG. 5for the convenience of description but not intended to limit the scope of the disclosure. Referring to bothFIG. 1andFIG. 5, the wireless communication device130includes a low-pass filter & sampler510, correlation operation devices520,530, and540, delay devices522,532, and542, adders550,560, and570, and a peak detector580.

As described above, the first BS110emits a first wireless signal. The first wireless signal includes a first cell132(for example, a pcell) having a first CC as its frequency band and a second cell134(for example, a scell) having a second CC as its frequency band. The first cell132includes a PDCCH136, and the PDCCH136contains information related to the second cell134(for example, a cell ID of the second cell134). The wireless communication device130can easily acquire synchronization of the first cell132. Thus, the wireless communication device130can obtain the individual ID and cell group ID of the second cell134according to the first cell132.

The second cell134includes a PSS and a SSS. The PSS depends on an individual ID of the second cell134, and the SSS depends on a cell group ID of the second cell134. Thus, after obtaining the individual ID and cell group ID of the second cell134, the wireless communication device130can acquire synchronization of the second cell134according to the cell group ID, the PSS and the SSS of the second cell134.

For example, the cell group ID has 168 possible values (0-167), the individual ID has 3 possible values (0, 1, and 2). The cell group ID of the second cell134can be obtained from BS110or BS120. The wireless communication device130can acquire synchronization according to a PSS sequence similar to a synchronization preamble, generate a SSS sequence according to the cell group ID, and acquire synchronization by using the SSS sequence. Namely, the wireless communication device performs a correlation operation on the SSS sequence and the SSS of the received wireless signal, performs a correlation operation on the PSS sequence and the PSS of the received wireless signal, and acquires synchronization by using the results of the correlation operations.

After the wireless communication device130receives the wireless signal, the low-pass filter & sampler510filters the wireless signal to remove carriers and sample the wireless signal. The correlation operation device520performs a correlation operation on the sampled signal and the PSS sequence. The correlation operation devices530and540perform a correlation operation on the sampled signal and the SSS sequence. To add up the operation results, the operation results are respectively delayed for different time periods by the delay devices522,532, and542. After the delayed signals are added up by the adders550,560, and570, the time points of the peaks are detected by the peak detector580to acquire synchronization. Namely, synchronization of the scell134can be easily acquired with the first BS110by using aforementioned operation results.

In the embodiment illustrated inFIG. 5, the two correlation operation devices530and540are adopted for respectively performing correlation operations on the SSS of the subframe 0 and the SSS of the subframe 1. However, the disclosure is not limited thereto, and a single correlation operation device may also be adopted. For example, a wireless network system working in the FDD mode is a typical example.

As described above, a wireless communication device can always acquire synchronization according to an extended PSS and/or a PSS of a second OFDM symbol even if the wireless communication device is located within a RE with serious interference. In addition, the wireless communication device may also acquire synchronization according to a cell ID, a PSS, and a SSS.