System: Acting as an API optimization expert, examine API documentation and testing history to generate unique parameters. Ensure the parameters are different from all previous attempts. Return only the parameter dictionary.
User: Analyze this API:
Endpoint: http://api.map.baidu.com/timezone/v1
Method: GET
Required: [{'name': 'ak', 'type': 'string', 'description': 'api_key', 'default': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV'}, {'name': 'location', 'type': 'string', 'description': '需查询时区的位置坐标', 'default': ''}, {'name': 'timestamp', 'type': 'int', 'description': '所需时间（用于判断夏令时）。以协调世界时 1970 年 1 月 1 日午夜以来的秒数表示（即Unix时间戳）', 'default': ''}]
Optional: [{'name': 'sn', 'type': 'string', 'description': '若用户所用ak的校验方式为sn校验时该参数必须', 'default': ''}, {'name': 'coord_type', 'type': 'string', 'description': '请求参数中坐标的类型', 'default': 'wgs84ll'}]
Test history: Initial Attempt 1:
Parameters: {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'location': '39.9042,116.4074', 'timestamp': 1633072800, 'sn': 'new_sn_value', 'coord_type': 'gcj02ll'}
Result: Failed
Analysis: Failed - possible issues: Unknown error occurred

Initial Attempt 2:
Parameters: {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'location': '34.0522,-118.2437', 'timestamp': 1696272000, 'sn': 'unique_sn_value_123', 'coord_type': 'bd09ll'}
Result: Failed
Analysis: Failed - possible issues: Unknown error occurred

Recent Attempt 3:
Parameters: {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'location': '48.8566,2.3522', 'timestamp': 1680000000, 'sn': 'different_sn_value_456', 'coord_type': 'wgs84ll'}
Result: Failed
Analysis: Failed - possible issues: Unknown error occurred

Recent Attempt 4:
Parameters: {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'location': '35.6895,139.6917', 'timestamp': 1690000000, 'sn': 'new_sn_value_789', 'coord_type': 'wgs84ll'}
Result: Failed
Analysis: Failed - possible issues: Unknown error occurred

Recent Attempt 5:
Parameters: {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'location': '40.7306,-73.9352', 'timestamp': 1672531199, 'sn': 'unique_sn_value_999', 'coord_type': 'wgs84ll'}
Result: Failed
Analysis: Failed - possible issues: Unknown error occurred

Previously used parameters: - {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'coord_type': 'wgs84ll', 'location': '48.8566,2.3522', 'sn': 'different_sn_value_456', 'timestamp': '1680000000'}
- {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'coord_type': 'gcj02ll', 'location': '39.9042,116.4074', 'sn': 'new_sn_value', 'timestamp': '1633072800'}
- {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'coord_type': 'wgs84ll', 'location': '35.6895,139.6917', 'sn': 'new_sn_value_789', 'timestamp': '1690000000'}
- {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'coord_type': 'bd09ll', 'location': '34.0522,-118.2437', 'sn': 'unique_sn_value_123', 'timestamp': '1696272000'}
- {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'coord_type': 'wgs84ll', 'location': '40.7306,-73.9352', 'sn': 'unique_sn_value_999', 'timestamp': '1672531199'}
- {'ak': 'hy8VOY8ik4LPjgHHfPFdbA9pE5rzWUwV', 'coord_type': 'wgs84ll', 'location': '51.5074,-0.1278', 'sn': 'another_unique_sn_value', 'timestamp': '1700000000'}

Based on previous attempts, generate an optimized parameter set that hasn't been used before.
Assistant: